Untitled

// ????? ?????????.
#include <iostream>
using namespace std;
int main()
{
	int c;
	cin >> c;
	unsigned long long a = 0;
	unsigned long long b = 1;
	while (c >= 1)
	{
		c -= 1;
		a = a + b;
		b = a - b;
	}
	cout << b;
	return 0;
}