
S = input()

S = [s for s in S]

ans = 0
while len(S) > 0:
    counter = 0
    for ix in range(len(S)):
        if ix+1 < len(S):
            if S[ix] != S[ix+1]:
                print(S)
                del S[ix]
                del S[ix]
                ans += 1
                counter += 1
    if counter == 0:
        break

print(ans*2)