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

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    ll N; cin >> N;
    vector<ll> dp(N + 1, 0);
    dp[0] = 1; dp[1] = 1;
    for(int i = 2; i <= N; i++) dp[i] = dp[i - 1] + dp[i - 2];
    cout << dp[N] << endl;
}