local mmi, mma = math.min, math.max
local mfl = math.floor

local function comp(a, b)
  return a < b
end

local function lower_bound(ary, x)
  local num = #ary
  if num == 0 then return 1 end
  if not comp(ary[1], x) then return 1 end
  if comp(ary[num], x) then return num + 1 end
  local min, max = 1, num
  while 1 < max - min do
    local mid = mfl((min + max) / 2)
    if comp(ary[mid], x) then
      min = mid
    else
      max = mid
    end
  end
  return max
end

local n, m = io.read("*n", "*n")
local a = {}
for i = 1, n do
  a[i] = io.read("*n")
end
local t = {}
for i = 1, n - 1 do
  t[i] = {}
end
local leftmin = false
local rightmax = false
for i = 1, m do
  local b = io.read("*n")
  local lb = lower_bound(a, b)
  if 1 == lb then
    if not leftmin then leftmin = b end
  elseif n < lb then
    rightmax = b
  else
    table.insert(t[lb - 1], b)
  end
end
local ret = 0
if leftmin then
  ret = ret + a[1] - leftmin
end
if rightmax then
  ret = ret + rightmax - a[n]
end
for i = 1, n - 1 do
  if 0 < #t[i] then
    local ti = t[i]
    local lenmax = mma(ti[1] - a[i], a[i + 1] - ti[#ti])
    for j = 1, #ti - 1 do
      lenmax = mma(lenmax, ti[j + 1] - ti[j])
    end
    ret = ret + a[i + 1] - a[i] - lenmax
  end
end
ret = tostring(ret * 1LL):gsub("LL", "")
print(ret)