import sys
input = sys.stdin.readline
S = list(map(lambda x: ord(x) - ord("a"), list(input())[: -1]))

if len(set(S)) == 1:
  if len(S) % 2: print(-1)
  else: print(0)
  exit(0)

if S != S[: : -1]:
  print(len(S))
  exit(0)

if len(S) != 3: print(len(S) - 2)
else: print(-1)