#include <bits/stdc++.h>
using namespace std;

void fast_io() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
}

int main() {
	fast_io();
	int a, b, c;
	cin >> a >> b >> c;
	long double cosa = (long double)(b * b + c * c - a * a) / (2 * b * c);
	long double sina = sqrtl(1 - cosa * cosa);
	long double ans = sina / 8;
	ans *= b * c;
	cout << fixed << setprecision(16) << ans << endl;
}