#include <iostream>
using namespace std;
long long f[1005];
int n;
int main()
{
	cin >> n;
	f[1] = 1;
	f[2] = 2;
	for (int i = 3;i <= n;i++)
	{
		f[i] = f[i - 1] + f[i - 2];
	}
	cout << f[n];
}