#include <bits/stdc++.h>

using namespace std;

#define LL long long

int main()
{
	int n;
	LL a[100000];
	a[0] = 0;
	a[1] = 1;

	cin >> n;
	int m;

	for (int i = 2; i <= n; i++)
	{
		a[i] = a[i - 1] + a[i - 2];
		m = i;
	}

	cout << a[m];


	return 0;
}