#include <iostream>
using namespace std;

int main()
{
	int n;
	unsigned long long int masu[51];
	masu[0] = masu[1] = 1;
	masu[2] = 2;
	cin >> n;
	for (int i = 2; i <= n; i++)
	{
		masu[i] = masu[i - 1] + masu[i - 2];
	}
	cout << masu[n] << endl;
}