#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int main()
{
	int N;
	cin >> N;
	vector<long long int> res(50, 0);
	res[0] = 1; 
	res[1] = 1;
	for( int i = 2; i <= N; i++ ) {
		res[i] = res[i-1] + res[i-2];
	}
	cout << res[N] << endl;

	return 0;
}