#include <bits/stdc++.h>
int main() {
  long long l3, l4, l5;
  std::cin >> l3 >> l4 >> l5;
  long double pi = 3.141592653589793238462643383279;
  long double v3 = 1.0 / 3.0 * l3 * l3 * sqrtl(3.0) / 4.0 * l3 * sqrtl(2.0 / 3);
  long double v4 = 1.0 / 3.0 * l4 * l4 * l4 * sqrtl(2) / 2;
  long double v5 = 1.0 / 3.0 * l5 * l5 * sqrtl(25 + 10 * sqrtl(5)) / 4 * l5 *
                   sqrtl(4 * sinl(pi / 5) * sinl(pi / 5) - 1) /
                   (2 * sinl(pi / 5));
  std::cout.precision(10);
  return std::cout << std::fixed << v3 + v4 + v5, 0;
}
