n = int(input())
ng_words = [input().strip() for _ in range(n)]

result = []
for i in range(n):
    chars = set()
    for word in ng_words:
        chars.add(word[i])
    if len(chars) == 2:
        result.append('a')  # 也可以选择 'b'
    else:
        if 'a' in chars:
            result.append('b')
        else:
            result.append('a')

print(''.join(result))