s = input().strip()

if s == s[::-1]:
    all_same = all(c == s[0] for c in s)
    if all_same:
        if len(s) % 2 == 0:
            print(0)
        else:
            print(-1)
    else:
        print(len(s) - 2)
else:
    print(len(s))