n = int(input())
A = list(map(int, input().split()))

lst = [261.6, 294.3, 327.0, 348.8, 392.4, 436.0, 490.5]
mi = float("inf")
ans = -1

for l in lst:
    tmp = []
    x = 44100 / l
    for i, a in enumerate(A[:int(2 * x)]):
        tmp.append((i % x, a))
    tmp.sort()
    ma = -1 << 30
    for i in range(int(2 * x - 1)):
        ma = max(ma, abs(tmp[i + 1][1] - tmp[i][1]))
        
    if ma < mi:
        mi = ma
        ans = l




print(["C4", "D4", "E4", "F4", "G4", "A4", "B4"][lst.index(ans)])