s = input()
if len(set(s)) == 1:
    if len(s) % 2 == 1:
        print(-1)
    else:
        print(0)
else:
    if s != s[::-1]:
        print(len(s))
    else:
        if len(s) == 3:
            print(-1)
        else:
            print(len(s) - 2)