S = input()
L = len(S)

for i in range(L):
    if S[i] != S[~i]:
        print(L)
        break

else:
    for i in range(L - 1):
        if S[i] != S[i + 1]:
            if L == 3:
                print(-1)
            else:
                print(L - 2)
            break

    else:
        if L % 2 == 0:
            print(0)
        else:
            print(-1)