#include <stdio.h>
#include <math.h>
int main()
{
	float a, b, c, P, Sp;
	scanf("%f%f%f", &a, &b, &c);
	P = (a + b + c)*0.5;
	Sp = sqrt(P * (P - a) * (P - b) * (P - c));
	printf("%.1lf", Sp);
	return 0;
}

没有想明白WA的原因，求解