#include<cmath>
#include<cstdio>
#include<string>
#include<iostream>
#include<algorithm>
#define rep(i,a,b) for(int i=a;i<=b;i++)
using namespace std;
long long n,m;
long long dfs(long long x){
    if(x==1||x==2)
        return 1; 
    return dfs(x-1)+dfs(x-2);
}
int main(){
    cin>>m>>n;
    cout<<dfs(n-m+1);
    return 0;
}