import sys
read=sys.stdin.buffer.read
readline=sys.stdin.buffer.readline
readlines=sys.stdin.buffer.readlines

s=readline().rstrip().decode()
n=len(s)
if n==1:
    print(s+s)
    exit()
import itertools
a0=[0]+list(itertools.accumulate([int(s[i]==s[n-1-i]) for i in range(n)]))
a1=[0, 0]+list(itertools.accumulate([int(s[i]==s[n-i]) for i in range(1, n)]))
a2=[0]+list(itertools.accumulate([int(s[i]==s[n-2-i]) for i in range(n-1)]))
if n%2==0 and a0[n]==n:
    print(s[:n//2]+'a'+s[n//2:])
    exit()
for i in range(n):
    if 2*i+1<n:
        if a0[i]==i and a1[n-i]-a1[i+1]==n-2*i-1:
            print(s[:n-i]+s[i]+s[n-i:])
            exit()
    else:
        if a0[n-1-i]==n-1-i and a2[i]-a2[n-1-i]==2*i+1-n:
            print(s[:n-1-i]+s[i]+s[n-1-i:])
            exit()
print("NA")