local s = io.read()
if #s == 1 then
  print(s .. s)
  os.exit()
elseif #s == 2 then
  print(s .. s:sub(1, 1))
  os.exit()
end
local n = #s
local hn = math.floor(n / 2)
local f1 = s:sub(1, hn)
local f2 = s:sub(n - hn + 1, n):reverse()
if n % 2 == 1 then
  local ngpos = false
  for i = 1, hn do
    if f1:sub(i, i) ~= f2:sub(i, i) then
      ngpos = i
      break
    end
  end
  if not ngpos then
    print(f1 .. string.rep(s:sub(hn + 1, hn + 1), 2) .. f1:reverse())
    os.exit()
  end
  local mid = s:sub(hn + 1, hn + 1)
  local v = mid == f2:sub(hn, hn)
  for i = ngpos + 1, hn do
    if f1:sub(i, i) ~= f2:sub(i - 1, i - 1) then
      v = false break
    end
  end
  if v then
    print(f1 .. mid .. f2:sub(ngpos, hn):reverse() .. f1:sub(1, ngpos):reverse())
    os.exit()
  end
  v = mid == f1:sub(hn, hn)
  for i = ngpos + 1, hn do
    if f2:sub(i, i) ~= f1:sub(i - 1, i - 1) then
      v = false break
    end
  end
  if v then
    print(f2 .. mid .. f1:sub(ngpos, hn):reverse() .. f2:sub(1, ngpos):reverse())
  else
    print("NA")
  end
else
  local ngpos = false
  for i = 1, hn do
    if f1:sub(i, i) ~= f2:sub(i, i) then
      ngpos = i
      break
    end
  end
  if not ngpos then
    print(f1 .. "a" .. f1:reverse())
    os.exit()
  end
  local v = true
  for i = ngpos + 1, hn do
    if f1:sub(i, i) ~= f2:sub(i - 1, i - 1) then
      v = false
      break
    end
  end
  if v then
    print(f1 .. f2:sub(ngpos, hn):reverse() .. f1:sub(1, ngpos):reverse())
    os.exit()
  end
  v = true
  for i = ngpos + 1, hn do
    if f2:sub(i, i) ~= f1:sub(i - 1, i - 1) then
      v = false
      break
    end
  end
  if v then
    print(f2 .. f1:sub(ngpos, hn):reverse() .. f2:sub(1, ngpos):reverse())
  else
    print("NA")
  end
end