local mod = 998244353
local mfl = math.floor
local function bmul(x, y)
  local x0, y0 = x % 31596, y % 31596
  local x1, y1 = mfl(x / 31596), mfl(y / 31596)
  return (x1 * y1 * 62863 + (x1 * y0 + x0 * y1) * 31596 + x0 * y0) % mod
end
local function badd(x, y) return (x + y) % mod end

local n = io.read("*n", "*l")
local s = io.read()
local z = {25}
for i = 2, n do
  z[i] = (z[i - 1] * 25) % mod
end
local ret = 0
local one = 0
for i = 1, n do
  local b = s:byte(i) - 96
  if b == 1 then
    one = one + 1
    if 1 < one then
      break
    end
  else
    if one == 0 then
      local v = 1
      if i < n then
        v = z[n - i]
      end
      ret = badd(ret, v)
      if i < n then
        v = bmul(b - 2, n - i)
        if i + 1 < n then
          v = bmul(v, z[n - i - 1])
        end
        ret = badd(ret, v)
      end
    else
      local v = b - 2
      if i < n then
        v = bmul(v, z[n - i])
      end
      ret = badd(ret, v)
    end
  end
end
print(ret)