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

int main(void) {
	// your code goes here
int a,b,c;
scanf ("%d%d%d",&a,&b,&c);
double  s;
s=0.5*(a+b+c);
double area;
area=sqrt (s*(s-a)*(s-b)*(s-c));
printf ("%f",area);


	return 0;
}