BOJ 1157

단어 공부

a = input().lower()

b = 'abcdefghijklmnopqrstuvwxyz'
c = []
for i in range(len(b)):
    c.append(a.count(b[i]))
    total = max(c)
if c.count(total) == 1:
    k = b[c.index(total)]
    print(k.upper())

else:
    print('?')