#include <stdio.h>
#include <math.h>

int main() {
	int a,b,c;
	scanf("%d %d %d",&a,&b,&c);
	
	double s,S;
	s = (a+b+c)/2.0;
	S = sqrt(s * (s-a) * (s-b) * (s-c));
	
	printf("%.3lf",S);
	
	return 0;
}