#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
using namespace std;
using ll = long long;

int main(){
    int n;
    cin >> n;
    
    vector<ll> dp(n+10);

    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;
}