#include <bits/stdc++.h>

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)
#define unless(p) if(!(p))
#define until(p) while(!(p))

using ll = std::int64_t;
using P = std::tuple<int,int>;

int N;
ll dp[55];

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    dp[0] = 1;
    dp[1] = 1;

    for(int i=2;i<=50;++i){
        dp[i] = dp[i - 1] + dp[i - 2];
    }

    std::cin >> N;

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