freq = [261.6, 294.3, 327.0, 348.8, 392.4, 436.0, 490.5]
word = ["C4", "D4", "E4", "F4", "G4", "A4", "B4"]
N = int(input())
x = list(map(int, input().split()))

S = 10 ** 18
ans = -1
for i, f in enumerate(freq):
    d = round(N / f)
    s = sum([(x[i] - x[(i + d) % N]) ** 2 for i in range(N)])
    if s < S:
        S = s
        ans = i
print(word[ans])