#include<iostream>
#include<vector>
using namespace std;
typedef long long ll;

int main(){
    ll N;
    cin >> N;
    vector<ll> dp(N+5);
    dp[0]=1;
    dp[1]=1;
    for(ll i=0;i<=N;i++){
        dp[i+2]=dp[i]+dp[i+1];
    }
    cout << dp[N] << endl;
}