lap3.bai1

#include<iostream>
using namespace std;

int	sumDownby2(int n) {
	if (n <= 1) {
		return n;
	}
	else {
		return n + sumDownby2(n - 2);
	}
}


int main() {


	cout << sumDownby2(0);



	system("pause");
	return 0;
}