#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int N;
    cin >> N;
    ll dp[N+1] = {1,1,2};
    rep(i,2,N+1){
        dp[i] = dp[i-1] + dp[i-2];
    }
    cout << dp[N] << endl;
}