#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<bits/stdc++.h>
#include<iostream>
using namespace std;
const int maxn=10005;/*精度位数,自行调整*/
//1.如果需要控制输出位数的话，在str()里面把len调成需要的位数
//2.很大的位数是会re的，所以如果是幂运算的话，如 计算x^p的位数n, n=p*log(10)x+1;(注意要加一）
//3.还可以加上qmul，取模的过程也就是str()，c_str()再搞一次
class bign
{
    //io*2 bign*5*2 bool*6
    friend istream& operator>>(istream&,bign&);
    friend ostream& operator<<(ostream&,const bign&);
    friend bign operator+(const bign&,const bign&);
    friend bign operator+(const bign&,int&);
    friend bign operator*(const bign&,const bign&);
    friend bign operator*(const bign&,int&);
    friend bign operator-(const bign&,const bign&);
    friend bign operator-(const bign&,int&);
    friend bign operator/(const bign&,const bign&);
    friend bign operator/(const bign&,int&);
    friend bign operator%(const bign&,const bign&);
    friend bign operator%(const bign&,int&);
    friend bool operator<(const bign&,const bign&);
    friend bool operator>(const bign&,const bign&);
    friend bool operator<=(const bign&,const bign&);
    friend bool operator>=(const bign&,const bign&);
    friend bool operator==(const bign&,const bign&);
    friend bool operator!=(const bign&,const bign&);
public:
    int len,s[maxn];
    bign()
    {
        memset(s,0,sizeof(s));
        len=1;
    }
    bign operator=(const char* num)
    {
        int i=0,ol;
        ol=len=strlen(num);
        while(num[i++]=='0'&&len>1)
            len--;
        memset(s,0,sizeof(s));
        for(i=0; i<len; i++)
            s[i]=num[ol-i-1]-'0';
        return *this;
    }
    bign operator=(int num)
    {
        char s[maxn];
        sprintf(s,"%d",num);
        *this=s;
        return *this;
    }
    bign(int num)
    {
        *this=num;
    }
    bign(const char* num)
    {
        *this=num;
    }
    string str() const
    {
        string res="";
        for(int i=0; i<len; i++)
            res=char(s[i]+'0')+res;
        if(res=="")
            res="0";
        return res;
    }
};
bool operator<(const bign& a,const bign& b)
{
    int i;
    if(a.len!=b.len)
        return a.len<b.len;
    for(i=a.len-1; i>=0; i--)
        if(a.s[i]!=b.s[i])
            return a.s[i]<b.s[i];
    return false;
}
bool operator>(const bign& a,const bign& b)
{
    return b<a;
}
bool operator<=(const bign& a,const bign& b)
{
    return !(a>b);
}
bool operator>=(const bign& a,const bign& b)
{
    return !(a<b);
}
bool operator!=(const bign& a,const bign& b)
{
    return a<b||a>b;
}
bool operator==(const bign& a,const bign& b)
{
    return !(a<b||a>b);
}
bign operator+(const bign& a,const bign& b)
{
    int up=max(a.len,b.len);
    bign sum;
    sum.len=0;
    for(int i=0,t=0;t||i<up; i++)
    {
        if(i<a.len)
            t+=a.s[i];
        if(i<b.len)
            t+=b.s[i];
        sum.s[sum.len++]=t%10;
        t/=10;
    }
    return sum;
}
bign operator+(const bign& a,int& b)
{
    bign c=b;
    return a+c;
}
bign operator*(const bign& a,const bign& b)
{
    bign res;
    for(int i=0; i<a.len; i++)
    {
        for(int j=0; j<b.len; j++)
        {
            res.s[i+j]+=(a.s[i]*b.s[j]);
            res.s[i+j+1]+=res.s[i+j]/10;
            res.s[i+j]%=10;
        }
    }
    res.len=a.len+b.len;
    while(res.s[res.len-1]==0&&res.len>1)
        res.len--;
    if(res.s[res.len])
        res.len++;
    return res;
}
bign operator*(const bign& a,int& b)
{
    bign c=b;
    return a*c;
}
//只支持大数减小数
bign operator-(const bign& a,const bign& b)
{
    bign res;
    int len=a.len;
    for(int i=0; i<len; i++)
    {
        res.s[i]+=a.s[i]-b.s[i];
        if(res.s[i]<0)
        {
            res.s[i]+=10;
            res.s[i+1]--;
        }
    }
    while(res.s[len-1]==0&&len>1)
        len--;
    res.len=len;
    return res;
}
bign operator-(const bign& a,int& b)
{
    bign c=b;
    return a-c;
}
bign operator/(const bign& a,const bign& b)
{
    int i,len=a.len;
    bign res,f;
    for(i=len-1; i>=0; i--)
    {
        f=f*10;
        f.s[0]=a.s[i];
        while(f>=b)
        {
            f=f-b;
            res.s[i]++;
        }
    }
    while(res.s[len-1]==0&&len>1)
        len--;
    res.len=len;
    return res;
}
bign operator/(const bign& a,int& b)
{
    bign c=b;
    return a/c;
}
bign operator%(const bign& a,const bign& b)
{
    int len=a.len;
    bign f;
    for(int i=len-1; i>=0; i--)
    {
        f=f*10;
        f.s[0]=a.s[i];
        while(f>=b)
            f=f-b;
    }
    return f;
}
bign operator%(const bign& a,int& b)
{
    bign c=b;
    return a%c;
}
bign& operator+=(bign& a,const bign& b)
{
    a=a+b;
    return a;
}
bign& operator-=(bign& a,const bign& b)
{
    a=a-b;
    return a;
}
bign& operator*=(bign& a,const bign& b)
{
    a=a*b;
    return a;
}
bign& operator/=(bign& a,const bign& b)
{
    a=a/b;
    return a;
}
bign& operator++(bign& a)
{
    a=a+1;
    return a;
}
bign& operator++(bign& a,int)
{
    bign t=a;
    a=a+1;
    return t;
}
bign& operator--(bign& a)
{
    a=a-1;
    return a;
}
bign& operator--(bign& a,int)
{
    bign t=a;
    a=a-1;
    return t;
}
istream& operator>>(istream &in,bign& x)
{
    string s;
    in>>s;
    x=s.c_str();
    return in;
}
ostream& operator<<(ostream &out,const bign& x)
{
    out<<x.str();
    return out;
}

int main(){
    int n,k,mask=1,l3;
    char s[maxn];
    bign l,tot,cur,b;
    scanf("%d %s",&n,s);
    tot = n; l = s; k = 1; b = 2;
    if(n==1){
        if(l==1) cout<<1;
        else cout<<-1;
        return 0;
    }else if(n==2){
        if(l<=3) cout<<l;
        else cout<<-1;
        return 0;
    }else if(n==3){
        l3 = 0;
        for(int i=l.len-1;i>=0;i--){
            l3 *= 10;
            l3 += l.s[i];
        }
        k = (l3-1)/3;
        b = 2; tot = 1;
        while(mask<=k){
            if(mask&k) tot *= b;
            b = b*b;
            mask <<= 1;
        }
        tot *= 2;
        tot = tot-2+l3-3*k;
        cout<<tot;
        return 0;
    }
    while(tot<l){
        ++k;
        tot += b*n-(b-1)*3;
        b *= 2;
    }
    k--; b /= 2;
    tot -= b*n-(b-1)*3;
    cout<<l-tot+b*2-2;
    return 0;
}

n, k = list(map(int, input().strip().split(' ')))
interval = [1, n]
current = 0

while (k - current + interval[0] - 1 > interval[1]):
    if interval[0] == interval[1]:
        print(-1)
        exit()
    current += interval[1] - interval[0] + 1
    interval[0] = interval[0] * 2 + 1
    interval[1] = interval[1] * 2 - 1
    
print(k - current + interval[0] - 1)

#include <iostream>

typedef unsigned long long int ull;

using namespace std;
ull n,k;

ull sum(ull i){
    return (n-3llu)*((1llu<<i)-1llu) +3llu*i;
}
int main(){
    long long int s_n,s_k; 
    scanf("%lld %lld",&s_n,&s_k);
    if(s_n<1 || s_k <1){

        cout<<-1;
        return 0;
    }
    n = (ull) s_n;
    k = (ull) s_k; 
        if(n <= 2llu) {
        if (k>2llu*n-1llu) 
            cout<<-1;
        else
            cout<<k;
        
        return 0;
    }
    ull i;
    for( i=1llu;;i<<=1llu){
        if(sum(i)>=k) break;
    }
    if(i == 1llu) {;
        cout<<k;
        return 0;
    }
    
    ull l = i/2llu +1llu,mid=i,r=(mid<<2llu)-l;
    while(l<r){
        if(l == mid) break;

        if(sum(mid)>=k){
            if(sum(mid-1)<k){
                l=mid;
                break;
            }else
                r = mid; 
        }
        else
            l = mid;
        mid = (l+r)/2llu;
    }
    i = l;
    cout<<(1llu<<i) -2llu -sum(i-1llu) + k;
    return 0;
}