#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int main(){
int a, b, c;
double answer,s;
scanf("%d%d%d",&a,&b,&c);
s=0.5*(a+b+c);
answer=sqrt(s*(s-a)*(s-b)*(s-c));
printf("%lf",answer);
system("pause");
return 0;
}