#include <bits/stdc++.h>

using namespace std;

long long dp[51];

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