#include <bits/stdc++.h>
int main(void) {
  int l3, l4, l5;
  double h3, h4, h5;
  scanf(" %d %d %d", &l3, &l4, &l5);
  double r3 = (1.0 * l3 * l3 * l3) / (6 * sqrt(2));
  double r4 = (sqrt(2) / 6.0) * (1.0 * l4 * l4 * l4);
  double r5 = (1.0 / 24.0) * (5 + sqrt(5)) * 1.0 * l5 * l5 * l5;
  printf("%.12lf\n", r3 + r4 + r5);
  return 0;
}
