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

ll N;
vector<ll> dp(55, 0);

int main(void){
    
    cin >> N;
    
    dp[0] = 1;
    for(int i = 0; i <= N; ++i) dp[i + 1] += dp[i], dp[i + 2] += dp[i];
    
    cout << dp[N] << endl;
    
    return 0;
}