s = input()
t = s[::-1]
n = len(s)//2
i = 0
while i < n and s[i]==t[i]: i += 1
ss = s[:i] + t[i] + s[i:]
tt = t[:i] + s[i] + t[i:]
if ss == ss[::-1]: print(ss)
elif tt == tt[::-1]: print(tt)
else: print("NA")