#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;

int main()
{
	double a, b, c, S, p, d;
	//scanf("%f%f%f", &a, &b, &c ); 
	/*cout << a << b << c<<endl;*/
	cin >> a >> b >> c;
		if (a + b > c && a + c > b && b + c > a)
		{
			p = (a + b + c) / 2;
			d = (p * (p - a) * (p - b) * (p - c));
			S = sqrt(d);
			printf("%.1lf\n", S);
		}
		else
		cout << "flase" << endl;
	
	return 0;
}