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

alphabets = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
for alph in alphabets:
    if S == alph * n:
        if n % 2 == 1:
            print(-1)
        else:
            print(0)
        exit()

print(n - 2)