#include<iostream>
using namespace std;

int Fibonazzi(int x) {
	/*if (x == 0)
		return 0;
	else if (x == 1)
		return 1;
	else
		return Fibonazzi(x - 1) + Fibonazzi(x - 2);*/
	if (x == 0)
		return 0;
	else if (x == 1)
		return 1;
	else {
		int result, num1, num2;
		result = num1 = 0;
		num2 = 1;

		for (int i = 1; i < x; i++) {
			result = num1 + num2;
			num1 = num2;
			num2 = result;
		}
		return result;
	}
}

int main() {
	int input = 0;
	cin >> input;
	cout << Fibonazzi(input) << endl;

	return 0;
}