#include <bits/stdc++.h>
using namespace std;
const long double pi = 3.1415926535897;
long long exp(long long base, long long power, int p) {
  if (!base) return 0;
  long long t = exp(base, power / 2, p);
  if (power & 1)
    return t * t * base % p;
  else
    return t * t % p;
}
void solve() {
  long double a[6], ans(0);
  cin >> a[3] >> a[4] >> a[5];
  for (int i = 3; i < 6; i++)
    ans += (i * pow(a[i], 3) * sqrt(1 - 1 / (4 * pow(sin(pi / i), 2))) /
            (12 * tan(pi / i)));
  cout << fixed << setprecision(15) << ans;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t--) {
    solve();
    cout << "\n";
  }
  return 0;
}
