#include <iostream>
using namespace std;

int main() {
    int N;
    cin >> N;
    long long int fib[101];
    fib[0] = 0;
    fib[1] = 1;

    if (N <= 1) {
        cout << fib[N];
        return 0;
    }
    for (int i = 2; i < N+1; i++) {
        fib[i] = (fib[i-2] + fib[i-1]);
    }
    cout << fib[N];
    return 0;
}