#include <iostream>
using namespace std;

long long fibonacci(int n) {
    if (n <= 1)
        return n;
    
    long long prev = 0, current = 1;
    for (int i = 2; i <= n; ++i) {
        long long next = prev + current;
        prev = current;
        current = next;
    }
    return current;
}

int main() {
    int n;
    cin >> n;
    cout << fibonacci(n + 1) << endl;
    return 0;
}