1654. Шифровка

1654_encryption.py

s = input()
ls = len(s)
stack = [s[0]]

i = 1
while i < ls:
    if len(stack) > 0:
        ch = stack.pop()
        if ch != s[i]:
            stack.append(ch)
            stack.append(s[i])
    else:
        stack.append(s[i])
    i += 1

print("".join(stack))