def is_palindrome(l, r):
    s_sub = s[l:r+1]
    return s_sub==s_sub[::-1]

s = input()

if is_palindrome(0, len(s)-1):
    if len(s)%2==0:
        print(s[:len(s)//2]+'a'+s[len(s)//2:])
    else:
        print(s[:len(s)//2]+s[len(s)//2]+s[len(s)//2:])
    exit()
    
l, r = 0, len(s)-1

while True:
    if s[l]==s[r]:
        l += 1
        r -= 1
    else:
        if is_palindrome(l+1, r):
            print(s[:r+1]+s[l]+s[r+1:])
        elif is_palindrome(l, r-1):
            print(s[:l]+s[r]+s[l:])
        else:
            print('NA')
        exit()