#include<bits/stdc++.h>
using namespace std; 
int main() { 
	int n; 
	cin >> n; 
	int prev1 = 1;
	int prev2 = 1;
	int current = 1; 
	if (n == 1 || n == 2) { 
		cout << 1 << endl; 
		return 0; 
	}
	for (int i = 3; i <= n; i++) { 
		current = prev1 + prev2;
		prev1 = prev2; 
		prev2 = current; 
	} 
	cout << current << endl; 
	return 0; 
}
/**************************************************************
	Problem: 1238
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/