S = list(input())

last = S.pop(0)
stack = [last]
can_pop = True
cnt = 0
for s in S:
    if last != s and can_pop:
        stack.pop()
        can_pop = False
        # stack.append(s) 読み捨て
        cnt += 2
    else:
        stack.append(s)
        last = s
        can_pop = True

print(cnt)
