#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;
	
}