백준 알고리즘 1157번 파이썬

small = 'abcdefghijklmnopqrstuvwxyz'
big = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
num = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

word = input()

for i in range(len(word)):
    for j in range(len(small)):
        if word[i] == small[j]:
            num[j] += 1

        if word[i] == big[j]:
            num[j] += 1
Max = 0
x = 0
for l in range(len(num)):

    if num[l] > Max:
        Max = num[l]
        find = big[l]
        x = Max
count = 0
for m in range(len(num)):
    if Max == num[m]:
        count += 1
        if count >= 2:
            find = '?'
            break

print(find)