#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,f[] = {1,1}; cin >> N;
    rep(i,N) f[i&1] = f[i&1] + f[!(i&1)];
    cout << f[N&1] << endl;
}