def main120():
    import sys
    S_org = input()
    S = []

    for s in range(len(S_org)):
        S.append(S_org[s])
    S = list(map(int, S))

    cont = True
    index = 0
    count = 0

    if len(S) == 1:
        print(0)
        sys.exit()

    else:
        while(cont):
            print(index)
            if S[index] == S[index+1]:
                index += 1
            else:
                count += 2
                S.pop(index)
                S.pop(index)
                if index > 0:
                    index -= 1

            if index == len(S) - 2:
                if S[index] != S[index+1]:
                    count += 2
                print(count)
                sys.exit()


main120(