S = input()
if S!=S[::-1]:
    print(len(S))
    exit()

for i in range(len(S)-1):
    if S[i]!=S[i+1]:
        if len(S)==3:
            print(-1)
            exit()
        else:
            print(len(S)-2)
            exit()
if len(S)%2==1:
    print(-1)
else:
    print(0)