n, m = read_line.split.map(&.to_i)
a = read_line.split.map(&.to_i)
b = read_line.split.map(&.to_i)
ans = 0
bi = 0
if b[0] < a[0]
  ans += a[0] - b[0]
  while bi < m && b[bi] < a[0]
    bi += 1
  end
end
(n - 1).times do |i|
  nbi = bi
  bs = [] of Int32
  while nbi < m && b[nbi] < a[i + 1]
    bs << b[nbi]
    nbi += 1
  end
  if !bs.empty?
    ds = [bs[0] - a[i], a[i + 1] - bs[-1]]
    (bs.size - 1).times do |j|
      ds << bs[j + 1] - bs[j]
    end
    ans += a[i + 1] - a[i] - ds.max
  end
  bi = nbi
end
if b[-1] > a[-1]
  ans += b[-1] - a[-1]
end
puts ans