#include <bits/stdc++.h>
using namespace std;
const long long inf = 1LL << 60;
const long double eps = 1e-14;
int main() {
  cout.precision(15);
  double l3, l4, l5;
  cin >> l3 >> l4 >> l5;
  cout << (pow(l3, 3) * 0.35355339059327373 + pow(l4, 3) * sqrt(0.5) +
           pow(l5, 3) * 0.9045084971874995) /
              3
       << endl;
}
