L = list(input())
L_ = []
a = L.pop(0)
cnt = 0

while True:
    if len(L) == 0:
        break
    else:
        b = L.pop(0)
    if a is not b:
        cnt += 1
        L = L_ + L
        L_ = []
        a = L.pop(0)
    elif a is b:
        L_.append(a)
        a = b
    # print(L_, a,  L)

print(cnt * 2)

