#include <bits/stdc++.h>
using namespace std;
int main() {
  double l3, l4, l5, v1, v2, v3, tv;
  double tan54 = tan(3.14159265358979323846264338327950 * 54.0 / 180.0),
         cos54 = cos(54.0 * 3.14159265358979323846264338327950 / 180.0);
  cin >> l3 >> l4 >> l5;
  v1 = l3 * l3 * l3 * sqrt(2) / 12.0;
  v2 = l4 * l4 * l4 * sqrt(2) / 6.0;
  v3 =
      (sqrt(1 - (1 / (4 * cos54 * cos54))) * l5 * l5 * l5 * 5.0 * tan54) / 12.0;
  tv = v1 + v2 + v3;
  printf("%.12f\n", tv);
  return 0;
}
