S = input()
cnt = [0]*26
f = 1
lenS = len(S)
for i in range(lenS//2):
    si, sj = S[i], S[lenS-1-i]
    f *= si==sj
    cnt[ord(si)-97] += 1
    cnt[ord(sj)-97] += 1
if lenS%2:
    s = S[lenS//2]
    cnt[ord(s)-97] += 1
if f:
    lst = [c for c in cnt if c>0]
    if len(lst)==1:
        print(-1 if lenS%2 else 0)
    else:
        if lenS==3:
            print(-1)
        else:
            print(lenS-2)
else:
    print(lenS)