#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
    int N;
    cin>>N;
    vector<long long> dp(N+1,0);

    dp[1] = 1;
    dp[2] = 2;

    for(int i=3;i<=N;i++){
        dp[i] = dp[i-1] + dp[i-2];
    }

    cout<<dp[N]<<endl;
}