local n, m = io.read("*n", "*n", "*l")
local s = {}
for i = 1, n do
  s[i] = io.read()
end
local function check(w)
  for i = 1, n do
    local skipped = false
    local si = s[i]
    for j = 1, m + 1 do
      local z = skipped and si:byte(j - 1) or si:byte(j)
      if w:byte(j) ~= z then
        if skipped then 
          return false
        else
          skipped = true
        end
      end
    end
  end
  return true
end
local c = 0
if n == 2 then
  for i = 1, m do
    if s[1]:byte(i) ~= s[2]:byte(i) then
      local w = s[1]:sub(1, i) .. s[2]:sub(i, m)
      if check(w) then
        c = c + 1
      end
      w = s[2]:sub(1, i) .. s[1]:sub(i, m)
      if check(w) then
        c = c + 1
      end
      break
    end
  end
else
  for i = 1, m do
    local t = {}
    local z = 0
    for j = 1, n do
      local b = s[j]:byte(i)
      if not t[b] then
        z = z + 1
        t[b] = {j}
      else
        table.insert(t[b], 0)
      end
    end
    if 2 < z then break end
    if z == 2 then
      local k1, v1 = next(t)
      local k2, v2 = next(t, k1)
      if #v1 == 1 then
        local w = s[k2]:sub(1, i) .. s[k1]:sub(i, m)
        if check(w) then c = c + 1 end
      else
        local w = s[k1]:sub(1, i) .. s[k2]:sub(i, m)
        if check(w) then c = c + 1 end
      end
      break
    end
  end
end
print(c)