#include <iostream> #include <string> #include <algorithm> #include <utility> #include <cmath> #include <cstdlib> #include <map> #include <set> #include <queue> #include <vector> #include <iomanip> #include <limits> using namespace std; int main() { long double a, b, c; cin >> a >> b >> c; long double s = (a + b + c) / 2; long double ans = s * (s - a) * (s - b) * (s - c); cout << fixed << setprecision(7); cout << sqrt(ans) / 4 << endl; }