#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a =  1 , b = 1 , c;
	cin >> c;
	int sum;
	for(int i = 3 ; i <= c ; i++)
	{
		sum = a + b;
		a = b;
		b = sum;
	}
	cout << b;
}