#include<iostream>
using namespace std;

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