#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    int dp[n+1];
    dp[0] = 0;
    dp[1] = 1;
    dp[2] = 2;
    dp[3] = 3;
    if (n < 4) {
        cout << n;
        return 0;
    }
    for (int i = 4;i <= n;i++) {
        dp[i] = dp[i-1] + dp[i-2];
    }
    cout << dp[n];
    return 0;
}