#include <iostream>

using namespace std;

void kvadrat() {
	int S, a, b;
	cin >> a >> b;
	S = a * b;
	cout << S;
}

void triangle() {
	int S, a, h;
	cin >> a >> h;
	S = (a * h) / 2;
	cout << S;
}

void circle() {
	int S, r;
	cin >> r;
	S = 3.14 * pow(r, 2);
	cout << S;
}

int main() {

	kvadrat();

	triangle();

	circle();

	system("pause");
	return 0;
}