#include <iostream>
using namespace std;

#define N 50

int n;
unsigned long long dpm[N+2];

unsigned long long dp()
{
	dpm[n] = 1;

	for ( int i = n - 1; i >= 0; i-- ) {
		dpm[i] = dpm[i + 1] + dpm[i + 2];
	}

	return dpm[0];
}

int main()
{
	cin >> n;

	cout << dp() << endl;

	return 0;
}