#include <iostream>
using namespace std;
long long int memo[101];
long long int fib(int n) {
    if (n <= 1) return n;
    if (memo[n] != 0) return memo[n];
    memo[n] = (fib(n-2) + fib(n-1));
    return memo[n];
}

int main() {
    int N;
    cin >> N;
    cout << fib(N);
}