P2437

#include<bits/stdc++.h>
#define int long long
using namespace std;
int a[100005];
signed main(){
	a[0]=0;
	a[1]=1;
	int n,m;
	cin>>n>>m;
	int x=m-n+1;
	for(int i=2;i<=x;i++){
		a[i]=a[i-1]+a[i-2];
	}
	cout<<a[x];
	return 0;
}