#include <stdio.h>

int main(void) {
	int a, b, c;
	scanf("%d%d%d", &a, &b, &c);
	float s, area_square;
	s = (a + b + c) / 2;
	area_square = s * (s - a) * (s - b) * (s - c);
	printf("%.0f", area_square);
	return 0;
}