#include <bits/stdc++.h>

using namespace std;

//著名的斐波纳契数列
int Fibonacci(int n) {
    if (n == 0) return 0;
    if (n == 1) return 1;
    return Fibonacci(n - 1) + Fibonacci(n - 2);
}

int main() {
    int n;
    cin >> n;
    cout << Fibonacci(n) << endl;
    return 0;
}