#include<stdio.h>
#include<math.h> 
#include<bits/stdc++.h>
using namespace std;void fun(double a,b,c)
{double p,c;p= (a+b+c)/2;c= sqrt(p*(p-a)*(p-b)*(p-c));printf("面积是：%lf",c);
}int main(){double a,b,c;scanf("%lf,%lf,%lf",&a,&b,&c);fun(a,b,c);	return 0;}