#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,c;
	double e,d;
	cin>>a>>b>>c;
	e=(a+b+c)/2*1.0;
	d=sqrt(e*(e-a)*(e-b)*(e-c));
	cout<<fixed<<setprecision(1)<<d;
	return 0;
}