s = input()
n = len(s)
assert 1 <= n <= 10 ** 6
u = set()
for i in range(n):
    if s[i] != s[n - i - 1]:
        print(n)
        exit()
    u.add(s[i])

if len(u) == 1:
    if n & 1:
        print(-1)
    else:
        print(0)
else:
    if n == 3:
        print(-1)
    else:
        print(n - 2)