import sys
INF = float('inf')
#10**20,2**63,float('inf')
MOD = 10**9 + 7
MOD2 = 998244353
from collections import defaultdict
def solve():
    def II(): return int(sys.stdin.readline())
    def LI(): return list(map(int, sys.stdin.readline().split()))
    def LC(): return list(input())
    def IC(): return [int(c) for c in input()]
    def MI(): return map(int, sys.stdin.readline().split())
    S = LC()
    N = len(S)
    C = defaultdict(lambda:0)
    Flag = True
    if N==3:
        if (S[0] == S[2]) and S[0] != S[1]:
            print(-1)
            exit()
    for n in range(N):
        C[S[n]] = 1
        if(S[n] != S[N-n-1]):
            Flag = False
    if not Flag:
        print(N)
        exit()

    #以下は回文
    if sum(list(C.values())) >=2:#2文字以上使われてたら，元の長さから良い感じに2個消せばいい．
        print(N-2)
        exit()

    #以下は使われる文字が1種類
    if N%2 == 1:
        print(-1)
    else:
        print(0)

    return
solve()
#sys.setrecursionlimit(10 ** 6)#再帰関数ではコメントにしないこと！！