#include <algorithm>
#include <cmath>
#include <iostream>
#include <numeric>
#include <queue>
#include <unordered_map>
#include <vector>
using namespace std;
using ll = long long;
#define rep(i, j, n) for (int i = j; i < (n); ++i)
#define rrep(i, j, n) for (int i = (n)-1; j <= i; --i)
#define all(a) a.begin(), a.end()
template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> &a) {
  for (size_t i = 0; i < a.size(); ++i) os << (i > 0 ? " " : "") << a[i];
  return os << '\n';
}
template <typename T>
std::istream &operator>>(std::istream &is, std::vector<T> &a) {
  for (T &x : a) { is >> x; }
  return is;
}

const double F[] = {261.6, 294.3, 327.0, 348.8, 392.4, 436.0, 490.5};
const char C[] = {'C', 'D', 'E', 'F', 'G', 'A', 'B'};
double a[44111];
int main() {
  cin.tie(0)->sync_with_stdio(0);
  int n;
  cin >> n;
  rep(i, 0, n) cin >> a[i];
  int mni = 0;
  double mn = 1e18;
  rep(j, 50, 180) {
    double s = 0;
    rep(i, 0, n) {
      double t = a[i] - a[(i + j) % n];
      s += t * t;
    }
    if (s < mn) {
      mn = s;
      mni = j;
    }
  }
  double f = (double)n / mni;
  double mf = 1e18;
  int ans = 0;
  rep(i, 0, 7) {
    if (abs(f - F[i]) < mf) {
      mf = abs(f - F[i]);
      ans = i;
    }
  }
  cout << C[ans] << '4' << '\n';
  return 0;
}