s = input()
if len(s)==1:
    print(-1)
else:
    n = len(s)
    a = s[:(n+1)//2]
    b = s[::-1][:(n+1)//2]
    if sum([s[0]==s[i]for i in range(n)])==n and a==b:
        if n%2==0:
            print(0)
        else:
            print(-1)
    elif a==b:
        if n>=4:
            print(n-2)
        else:
            print(-1)
    else:
        print(n)