#include <bits/stdc++.h>
using namespace std;
long double fx(long double n, long double l) {
  long double theta =
      ((360.0 / n) * 3.14159265358979323846264338327950288) / 180.0;
  long double ans = (((n * l * l * l) * sin(theta)) *
                     sqrt(4 * pow(sin(theta / 2.0), 2) - 1)) /
                    (48 * pow(sin(theta / 2), 3));
  return ans;
}
int main() {
  long double l1, l2, l3, ans;
  cin >> l1 >> l2 >> l3;
  ans = fx(3, l1) + fx(4, l2) + fx(5, l3);
  printf("%.15Lf", ans);
  return 0;
}
