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 n = io.read("*n", "*l")
local s = io.read()
local t = {}
for i = 1, n do
  t[i] = s:sub(i, i)
end
for i = 1, n - 1 do
  if t[i] == t[i + 1] and t[i] ~= "?" then
    print(0) os.exit()
  end
end
for i = 1, n - 2 do
  if t[i] == t[i + 2] and t[i] ~= "?" then
    print(0) os.exit()
  end
end
local ret = 1
for i = 1, n do
  local c = 0
  if t[i] == "?" then
    if 2 < i then
      c = c + 1
    end
    if 1 < i then
      c = c + 1
    end
    if i <= n - 1 then
      if t[i + 1] ~= "?" then
        local f = true
        if 2 < i and t[i - 2] == t[i + 1] then f = false end
        if 1 < i and t[i - 1] == t[i + 1] then f = false end
        if f then c = c + 1 end
      end
    end
    if i <= n - 2 then
      if t[i + 2] ~= "?" then
        local f = true
        if 2 < i and t[i - 2] == t[i + 2] then f = false end
        if 1 < i and t[i - 1] == t[i + 2] then f = false end
        if t[i + 1] == t[i + 2] then f = false end
        if f then c = c + 1 end
      end
    end
    -- print(26 - c)
    ret = bmul(ret, 26 - c)
  end
end
print(ret)