#include<bits/stdc++.h>
using namespace std;
string s;
int a[10005];
int jz,len;
int plus_(int n){
    int carry=0;
    int c[10005]={0};
    for(int i=0;i<n;i++){
        c[i]=a[i]+a[n-i-1]+carry;
        if(c[i]>=jz){
            c[i]=c[i]%jz;
            carry=1;
        }
        else carry = 0;
        //cout<<c[i]<<" ";
    }
    if(carry==1){
        n++;
        c[n-1]=1;
    }
    //cout<<c[n-1];
    for(int i=0;i<n;i++){
        a[i]=c[i];
    }
    return n;
}
bool judge(int a[]){
    for(int i=0;i<len/2;i++){
        if(a[i]!=a[len-i-1]) return false;
    }
    return true;
}
int main(){
    cin>>jz>>s;
    len = s.size();
    for(int i=0;i<len;i++){
        if(s[i]-'0'<10) a[i]=s[i]-'0';
        else if(s[i]-'A'<=5) a[i]=s[i]-'A'+10;
    }
    //len = plus_(len);
    int cnt=0;
    while(cnt<=30){
        if(judge(a)){
            cout<<"STEP="<<cnt<<endl;
            return 0;
        }
        else{
            cnt++;
            len = plus_(len);
            //print();
        }
    }
    cout<<"Impossible"<<endl;
    return 0;
}