#include<iostream>
#include<algorithm>
#include<math.h>
using namespace std;
int main()
{
	double a,b,c,p,Area;
	cout<<"请输入三角形的三个边长："<<endl;
	cin>>a>>b>>c;
	p=(a+b+c)/2;
	Area=sqrt(p*(p-a)*(p-b)*(p-c));
	cout<<Area<<endl;
    return 0;
	
}