s = input().strip()

head = 0
tail = len(s) - 1

while head < tail:
    if s[head] == s[tail]:
        head += 1
        tail -= 1
        continue
    news = s[:head] + s[tail] + s[head:]
    if news == news[::-1]:
        print(news)
        break
    news = s[:tail+1] + s[head] + s[tail + 1:]
    if news == news[::-1]:
        print(news)
        break
    print('NA')
    break
else:
    mid = len(s) // 2
    news = s[:mid] + s[mid] + s[mid:]
    print(news)