题解 | #密码截取#

shuru=input()
chucun=[[]]
changdu1=1
changdu2=1
for i2 in range(len(shuru)-1):
    if shuru[i2]==shuru[i2+1] :
        chucun[0].append(i2)
for k in range(1,len(shuru)):
    chucun.append([])
    for i in chucun[k-1]:
        if i-k>=0 and i+1+k<len(shuru):
            if shuru[i-k]==shuru[i+1+k]:
                chucun[k].append(i)
    if chucun[k]==[]:
        changdu1=2*(k-1)+2
        break
chucun1=[[]]
for i1 in range(len(shuru)):
    chucun1[0].append(i1)
for k1 in range(1,len(shuru)):
    chucun1.append([])
    for i in chucun1[k1-1]:
        if i-k1>=0 and i+k1<len(shuru):
            if shuru[i-k1]==shuru[i+k1]:
                chucun1[k1].append(i)
    if chucun1[k1]==[]:
        changdu2=1+2*(k1-1)
        break
print(max(changdu1,changdu2))