#include<bits/stdc++.h>
using namespace std;
int a[10005];
int main()
{
    int x,y,sum=0;
    cin>>x>>y;
    for(int i=1;i<=y;i++)
        cin>>a[i];
    a[1]=1;
    a[2]=1;
    for(int i=3;i<=y;i++)
        a[i]=a[i-2]+a[i-1];
    for(int i=x;i<=y;i++)
        sum+=a[i];
    cout<<sum<<endl;
    return 0;
} 

#include<bits/stdc++.h>
using namespace std;
int a,b,sum=0,fei[1000005]{0,1,1};
int main()
{
    cin>>a>>b;
    for(int i=3;i<=b;i++)
        fei[i]=fei[i-1]+fei[i-2];
    for(int i=a;i<=b;i++)
        sum=sum+fei[i];
    cout<<sum;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
int n,a,b,c,i;
cin>>n;
a=1;
b=1;
i=3;
while(i<=n)
{
c=a+b;
a=b;
b=c;
i=i+1;
}
cout<<a+b+c-1;
return 0;
}