#include <bits/stdc++.h>
using namespace std;
int l[7];
int main() {
  scanf("%d%d%d", &l[3], &l[4], &l[5]);
  double a, A, ap, r, anw = 0;
  for (int n = 3; n <= 5; n++) {
    a = acos(-1) / n;
    A = 1.0 * n / 4 * l[n] * l[n] / tan(a);
    ap = A * 2 / n / l[n];
    r = ap / cos(a);
    anw += A * sqrt(l[n] * l[n] - r * r) / 3;
  }
  printf("%.10lf", anw);
}
