#include<iostream>
using namespace std;
long long fibonacci(long long n)
{
	if (n == 1)
		return 1;
	if (n == 2)
		return 2;
	if (n != 1 && n != 2)
		return fibonacci(n - 1) + fibonacci(n - 2);	
}
int main()
{
	long long N;
	cin >> N;
	cout << fibonacci(N);
	return 0;
}