#include <bits/stdc++.h>
int main() {
  double a, b, c;
  while (~scanf("%lf %lf %lf", &a, &b, &c)) {
    double ans = (pow(a, 3) * sqrt(2)) / 12 + (pow(b, 3) * sqrt(2)) / 6 +
                 (pow(c, 3) * (5 + sqrt(5))) / 24;
    printf("%.12f\n", ans);
  }
}
