S = input()
N = len(S)
i = 0
j = N - 1
f = 0
while i < N and 0 <= j:
    if S[i] == S[j]:
        i += 1
        j -= 1
    elif f < 1 and S[i + 1] == S[j]:
        S = S[:j + 1] + S[i] + S[j + 1:]
        N += 1
        j += 1
        f += 1
    elif f < 1 and S[i] == S[j - 1]:
        S = S[:i] + S[j] + S[i:]
        N += 1
        j += 1
        f += 1
    else:
        print("NA")
        exit()
if f == 0:
        print(S[:N // 2] + S[N // 2] + S[N // 2:])

else:
    print(S)