#include <bits/stdc++.h>

using namespace std;

long long fb[50];

long long fib(int n) {
    if (fb[n]) return fb[n];
    if (n < 2) return 1;
    return fb[n] = fib(n - 1) + fib(n - 2);
}

int main() {
    int n;
    cin >> n;

    cout << fib(n) << endl;
    return 0;
}