#include <iostream>
using namespace std;
using ll = long long;

ll dp[55];
int n;

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