#include<bits/stdc++.h>
using namespace std;

long long n,dp[75];

int main(){
	cin>>n;
	dp[0] = dp[1] = 1;
	for(int i = 2;i<=n;i++){
		dp[i] = dp[i-1]+dp[i-2];
	}
	cout<<dp[n];
	return 0;
}