mutate strings

word_one = input()
word_two = input()

for letter in range(len(word_one)):
    if word_one[letter] != word_two[letter]:
        for word_two_index in range(0, letter + 1):
            print(word_two[word_two_index], end="")

        for word_one_index in range(letter + 1, len(word_one)):
            print(word_one[word_one_index], end="")

        print()