local n = io.read("*n")
local x, y = {}, {}
local xidx, yidx = {}, {}
for i = 1, n do
  x[i], y[i] = io.read("*n", "*n")
  xidx[i], yidx[i] = i, i
end
table.sort(xidx, function(a, b) return x[a] < x[b] end)
table.sort(yidx, function(a, b) return y[a] < y[b] end)
local edge = {}
for i = 1, n - 1 do
  local v1, v2 = xidx[i], xidx[i + 1]
  edge[i] = {v1, v2, x[v2] - x[v1]}
end
for i = 1, n - 1 do
  local v1, v2 = yidx[i], yidx[i + 1]
  edge[n - 1 + i] = {v1, v2, y[v2] - y[v1]}
end

local function uf_initialize(n)
  local parent = {}
  for i = 1, n do parent[i] = i end
  return parent
end

local function uf_findroot(idx, parent)
  local idx_update = idx
  while parent[idx] ~= idx do
    idx = parent[idx]
  end
  while parent[idx_update] ~= idx do
    parent[idx_update], idx_update = idx, parent[idx_update]
  end
  return idx
end

local function kruskal(n, line)
  table.sort(line, function(a, b) return a[3] < b[3] end)
  local parent = uf_initialize(n)
  local totalcost = 0
  local used = 0
  local linenum = #line
  for i = 1, linenum do
    local c, i1, i2 = line[i][3], line[i][1], line[i][2]
    local r1, r2 = uf_findroot(i1, parent), uf_findroot(i2, parent)
    parent[i1], parent[i2] = r1, r2
    if r1 ~= r2 then
      parent[r2] = r1
      parent[i2] = r1
      totalcost = totalcost + c
      used = used + 1
      if used == n - 1 then break end
    end
  end
  return totalcost
end

print(kruskal(n, edge))
