#include <bits/stdc++.h>
using namespace std;
const int mod = 100;
const int inf = 1e9 + 9;
const int MOD = 1e9 + 696969;
const unsigned long long int INF = 4e18 + 3;
int n, m, d;
unsigned long long int silnia[15];
int space[20];
unsigned long long int dwumian(unsigned long long int n,
                               unsigned long long int k) {
  for (int i = 0; i <= 10; ++i) space[i] = 0;
  for (unsigned long long int i = 1; i <= k; ++i) space[i] = 1;
  unsigned long long int gora = 1;
  unsigned long long int pol = (n - k);
  for (unsigned long long int i = n; i > pol; --i) {
    gora = gora * i;
    for (unsigned long long int j = 1; j <= k; ++j)
      if (space[j] && (gora % j == 0)) space[j]--, gora /= j;
  }
  return gora;
}
double wynik;
int main() {
  double a, b, c;
  cin >> a >> b >> c;
  long double result = sqrt(2) * a * a * a;
  result /= 12;
  a = b;
  long double H = sqrt(a * a * 0.5);
  result += (a * a * H / 3);
  a = c;
  long double prw = sqrt(25 + (10 * sqrt(5)));
  long double pp = (a * a * 0.25 * prw);
  prw = (sqrt(50 + 10 * sqrt(5)) * 0.1);
  long double D = a * prw;
  H = sqrt(a * a - D * D);
  result += (pp * H / 3);
  wynik = result;
  printf("%.15lf", wynik);
}
