import sys
input=lambda: sys.stdin.readline().rstrip()
S=input()
n=len(S)

def chk(T):
  m=len(T)
  for i in range(m//2):
    if T[i]!=T[m-1-i]:
      return False
    else:
      continue
  else:
    return True

for i in range(n//2):
  if S[i]==S[n-1-i]:
    continue
  else:
    S1=S[:i]+S[n-1-i]+S[i:]
    S2=S[:n-i]+S[i]+S[n-i:]
    if chk(S1):
      print(S1)
    elif chk(S2):
      print(S2)
    else:
      print("NA")
    break
else:
  if n%2:
    print("NA")
  else:
    print(S[:n//2]+"a"+S[n//2:])