#include <bits/stdc++.h>
using namespace std;
const int INF = 1 << 30;
const long long LLINF = 1LL << 62;
const int mod = 1000000007;
long long l;
long double ll, r, ans, ar, p, h, PI;
int main() {
  PI = atan(1) * 4.0;
  cin >> l;
  ll = l;
  ans += ll * ll * ll * sqrt(2) / 12.0;
  cin >> l;
  ll = l;
  ans += ll * ll * ll * sqrt(2) / 6.0;
  cin >> l;
  ll = l;
  r = sqrt(ll * ll / (2.0 * (1.0 - cos(72.0 * PI / 180.0))));
  p = (2.0 * r + ll) / 2.0;
  ar = sqrt(p * (p - r) * (p - r) * (p - ll));
  ar *= 5;
  h = sqrt(ll * ll - r * r);
  ans += ar * h / 3.0;
  cout << fixed << setprecision(15) << ans;
  return 0;
}
