#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <array>
#include <map>
#include <stack>
#include <queue>
#include <set>

using namespace std;

int main() {

    int N;
    cin >> N;

    long dp[51];

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

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

    cout << dp[N] << "\n";
    return 0;
}