#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <numeric>
#include <string>
using namespace std;

int ceil(int a, int b){
    if (a % b){
        return a/b + 1;
    }else
        return a/b;
}
int main(){
    int n;
    cin >> n;

    long long dp[51];
    dp[0] = 0;
    dp[1] = 1;
    dp[2] = 2;

    for(int i = 3; i< 51; i++){
        dp[i] = dp[i-1] + dp[i-2];
    }
    cout << dp[n] << endl;
}