f = [261.6, 294.3, 327.0, 348.8, 392.4, 436.0, 490.5]
ans = ['C4', 'D4', 'E4', 'F4', 'G4', 'A4', 'B4']
n = int(input())
a = list(map(int, input().split()))
res = -1
d = -1
for i in range(7):
    t = int(n // f[i])
    dd = 0
    for j in range(1000):
        dd += abs(a[j] - a[j + t])
    if d == -1 or dd < d:
        d = dd
        res = i
print(ans[res])