#include <iostream>

using namespace std;
using LL = long long;
using ULL = unsigned long long;

LL dp[52];

int main() {
    int N;
    cin >> N;

    dp[0] = 1;
    for (int i = 0; i <= N - 1; i++) {
        dp[i + 1] += dp[i];
        dp[i + 2] += dp[i];
    }

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