def runlegth(S):
    cnt = 1
    d = []
    for i in range(len(S)-1):
        if S[i] == S[i+1]:
            cnt += 1
        else:
            d.append(cnt)
            cnt = 1
    d.append(cnt)
    return d
def main():
    S = input()
    D = runlegth(S)
    first = 0
    second = 0
    ans = 0
    for i in range(len(D)):
        if i % 2 == 0:
            first += D[i]
            ans = max(ans, min(first,second))
            if D[i] >= second:
                second = 0
        else:
            second += D[i]
            ans = max(ans, min(first,second))
            if D[i] >= first:
                first = 0

    print(ans * 2)


if __name__ == "__main__":
    main()