class RollingHash():
    def __init__(self, s):
        self._mod = 2 ** 31 - 1
        self._base = 4649
        
        n = len(s)
        self.h = [0] * (n + 1)
        self.pw = [1] * (n + 5)
 
        for i in range(n):
            self.h[i + 1] = self.h[i] * self._base + ord(s[i])
            self.h[i + 1] %= self._mod
 
        for i in range(n + 4):
            self.pw[i + 1] = self.pw[i] * self._base
            self.pw[i + 1] %= self._mod
            
        """
        s[l:r]のhash値
        """
    def get(self, l, r):
        return (self.h[r] - self.h[l] * self.pw[r - l]) % self._mod
    
S1 = list(input())
S2 = S1[::-1]
R1 = RollingHash(S1)
R2 = RollingHash(S2)
N = len(S1)
pw = R1.pw
mod = R1._mod
for i in range(N + 1):
    for s in range(26):
        si = s + ord("a")
        v1 = R1.get(0, i) * pw[N - i + 1] + R1.get(i, N) + si * pw[N - i]
        v2 = R2.get(0, N - i) * pw[i + 1] + R2.get(N - i, N) + si * pw[i]
        if (v1 - v2) % mod == 0:
            ans = S1[:i] + [chr(ord("a") + s)] + S1[i:]
            print(*ans, sep="")
            exit()
            
print("NA")