S = gets.chomp
RS = S.reverse
N = S.size

if S == RS
  l = N / 2
  S.insert(l, S[l])

  puts S
else
  idx = (0...N).find { |i| S[i] != RS[i] }
  r_idx = N - idx - 1
  s = S.dup
  s.insert(r_idx + 1, S[idx])
  rs = S.dup
  rs.insert(idx, S[r_idx])

  if s == s.reverse
    puts s
  elsif rs == rs.reverse
    puts rs
  else
    puts 'NA'
  end
end