UVa 10347 - Medians

// UVa 10347 - Medians

#include <math.h>
#include <cmath>
#include <iostream>
#include <stdio.h>
using namespace std;

int main() {
	double m1, m2, m3;
	while (cin >> m1 >> m2 >> m3) {
		m1 = abs(m1);
		m2 = abs(m2);
		m3 = abs(m3);
		double o = (m1 + m2 + m3) / 2;
		double D = o * (o - m1) * (o - m2) * (o - m3);
		double area = (D <= 0) ? -1 : (4.0 / 3) * sqrt(D);
		printf("%.3f\n", area);
	}
	return 0;
}