#include"bits/stdc++.h"
//#include<bits/stdc++.h>
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
typedef long long ll;
//const int mod = 1e9 + 7;

ll dp[52];

int main() {
	int n;
	cin >> n;
	dp[1] = 1; dp[2] = 2;
	rep(i, 3, 51) {
		dp[i] = dp[i - 1] + dp[i - 2] ;
	}
	print(dp[n]);
	return 0;
}