#include <iostream>
using namespace std;

int getSum(int n);

int main() {

    int n;
    cin >> n;

    cout << getSum(n) << endl;

    return 0;
}

int getSum(int n) {

    // write your code here......
    if (n < 3) {
        return 1;
    } else {
        return getSum(n - 1) + getSum(n - 2);
    }

}