#include <iostream>
using namespace std;

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