import sys

sys.setrecursionlimit(10 ** 6)
from bisect import *
from collections import *
from heapq import *

int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def SI(): return sys.stdin.readline()[:-1]
def MI(): return map(int, sys.stdin.readline().split())
def MI1(): return map(int1, sys.stdin.readline().split())
def MF(): return map(float, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LF(): return list(map(float, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
dij = [(0, 1), (1, 0), (0, -1), (-1, 0)]

def main():
    def dfs(i,j,ins=-1,c=''):
        if i>=j:
            if ins==-1:return s[:n//2]+s[n//2]+s[n//2:]
            else:return s[:ins]+c+s[ins:]
        if s[i]==s[j]:return dfs(i+1,j-1,ins,c)
        elif ins==-1:
            ret=dfs(i,j-1,i,s[j])
            if ret:return ret
            ret=dfs(i+1,j,j+1,s[i])
            if ret: return ret
        return ""

    s=SI()
    n=len(s)
    ans=dfs(0,n-1)
    if ans:print(ans)
    else:print("NA")

main()