def o2(f, r, m):
    flag = False
    i = 0
    j = 0
    af = []
    ar = []

    while i < len(f):
        if f[i] == r[j]:
            af.append(f[i])
            ar.append(r[j])
            i += 1
            j += 1
        else:
            if flag:
                return 'NA'
            flag = True
            af.append(r[j])
            ar.append(r[j])
            j += 1
    af += r[j:]
    ar += r[j:]

    return ''.join(af) + m + m + ''.join(ar[::-1])


def odd(s):
    L = len(s) >> 1

    if L == 0:
        return s + s

    m = s[L]
    f = s[:L]
    l = s[L + 1:]
    r = l[::-1]

    if f == r:
        return f + m + m + l

    if m != f[-1] and m != l[0]:
        return 'NA'

    if m == f[-1]:
        return o2(f[:-1], r, m)
    elif m == r[-1]:
        return o2(r[:-1], f, m)


def even(s):
    L = len(s) >> 1
    f = s[:L]
    l = s[L:]
    r = l[::-1]

    af = []
    ar = []
    flag = False

    i = 0
    j = 0

    while True:
        if i == j == L:
            if not flag:
                af.append('x')
                break
        elif i == L:
            ar.append(r[j:])
            break
        elif j == L:
            af.append(f[i:])
            break

        if f[i] == r[j]:
            af.append(f[i])
            ar.append(r[j])
            i += 1
            j += 1
        else:
            if flag:
                return 'NA'
            flag = True
            if i == j == L - 1:
                af.append(r[j])
                af.append(f[i])
                ar.append(r[j])
                break
            elif f[i] == r[j + 1]:
                af.append(r[j])
                af.append(f[i])
                ar.append(r[j])
                ar.append(r[j + 1])
                i += 1
                j += 2
            elif f[i + 1] == r[j]:
                af.append(f[i])
                af.append(f[i + 1])
                ar.append(f[i])
                ar.append(r[j])
                i += 2
                j += 1
            else:
                return 'NA'

    return ''.join(af) + ''.join(ar[::-1])


def solve(s):
    if len(s) % 2 == 0:
        ans = even(s)
    else:
        ans = odd(s)

    print(ans)


def main():
    s = input()
    solve(s)


if __name__ == '__main__':
    main()