#include <bits/stdc++.h>
using namespace std;
int main() {
  double l3, l4, l5, V3, V4, V5;
  cin >> l3 >> l4 >> l5;
  V3 = (sqrt(2) * l3 * l3 * l3) / 12;
  V4 = (l4 * l4 * l4 * sqrt(2)) / 6;
  V5 = (l5 * l5 * l5 * (5 + sqrt(5))) / 24;
  printf("%.10f\n", V3 + V4 + V5);
  return 0;
}
