#include <bits/stdc++.h>

std::array<double, 7> const freqs = {261.6, 294.3, 327.0, 348.8, 392.4, 436.0, 490.5};

int main() {
  int N;
  std::cin >> N;
  std::vector<int> A(N);
  for (int& e : A) { std::cin >> e; }

  double mn = std::numeric_limits<double>::max();
  int ans = -1;
  for (int t = 0; t < 7; ++t) {
    int w = int(std::round(N / freqs[t]));

    double avg = 0;
    for (int i = 0; i + w < N; ++i) { avg += A[i] - A[i + w]; }
    avg /= N - w;

    double cur = 0;
    for (int i = 0; i + w < N; ++i) { cur += (A[i] - A[i + w] - avg) * (A[i] - A[i + w] - avg); }
    if (cur < mn) {
      mn = cur;
      ans = t;
    }
  }
  std::cout << "CDEFGAB"[ans] << "4\n";
}