local mfl, mce, mmi = math.floor, math.ceil, math.min
local SegTree = {}
SegTree.updateAll = function(self)
  for i = self.stagenum - 1, 1, -1 do
    for j = 1, self.cnt[i] do
      self.stage[i][j] = self.func(self.stage[i + 1][j * 2 - 1], self.stage[i + 1][j * 2])
    end
  end
end
SegTree.create = function(self, n, func, emptyvalue)
  self.func, self.emptyvalue = func, emptyvalue
  local stagenum, mul = 1, 1
  self.cnt, self.stage, self.size = {1}, {{}}, {}
  while mul < n do
    mul, stagenum = mul * 2, stagenum + 1
    self.cnt[stagenum], self.stage[stagenum] = mul, {}
  end
  for i = 1, stagenum do self.size[i] = self.cnt[stagenum + 1 - i] end
  self.stagenum = stagenum
  -- for i = 1, #ary do self.stage[stagenum][i] = ary[i] end
  -- for i = #ary + 1, mul do self.stage[stagenum][i] = emptyvalue end
  for i = 1, mul do self.stage[stagenum][i] = emptyvalue end
  self:updateAll()
end
SegTree.getRange = function(self, left, right)
  if left == right then return self.stage[self.stagenum][left] end
  local start_stage = 1
  while right - left + 1 < self.size[start_stage] do
    start_stage = start_stage + 1
  end
  local ret = self.emptyvalue
  local t1, t2, t3 = {start_stage}, {left}, {right}
  while 0 < #t1 do
    local stage, l, r = t1[#t1], t2[#t1], t3[#t1]
    table.remove(t1) table.remove(t2) table.remove(t3)
    local sz = self.size[stage]
    if (l - 1) % sz ~= 0 then
      local newr = mmi(r, mce((l - 1) / sz) * sz)
      table.insert(t1, stage + 1) table.insert(t2, l) table.insert(t3, newr)
      l = newr + 1
    end
    if sz <= r + 1 - l then
      ret = self.func(ret, self.stage[stage][mce(l / sz)])
      l = l + sz
    end
    if l <= r then
      table.insert(t1, stage + 1) table.insert(t2, l) table.insert(t3, r)
    end
  end
  return ret
end
SegTree.setValue = function(self, idx, value, silent)
  self.stage[self.stagenum][idx] = value
  if not silent then
    for i = self.stagenum - 1, 1, -1 do
      local dst = mce(idx / 2)
      local rem = dst * 4 - 1 - idx
      self.stage[i][dst] = self.func(self.stage[i + 1][idx], self.stage[i + 1][rem])
      idx = dst
    end
  end
end
SegTree.new = function(n, func, emptyvalue)
  local obj = {}
  setmetatable(obj, {__index = SegTree})
  obj:create(n, func, emptyvalue)
  return obj
end

local mma, mmi = math.max, math.min
local n = io.read("*n")
local l, r = {}, {}
local s_idx = {}
for i = 1, n do
  l[i], r[i] = io.read("*n", "*n")
  s_idx[i] = i
end
table.sort(s_idx, function(x, y)
  if l[x] == l[y] then
    return r[x] < r[y]
  else
    return l[x] < l[y]
  end
end)
local lmin_idx = s_idx[1]
-- local rmax_idx = s_idx[n] == lmin_idx and s_idx[n - 1] or s_idx[n]
local rmax_idx, tmpscore = 0, 0
for i = 1, n do
  if lmin_idx ~= i then
    if rmax_idx == 0 then
      rmax_idx = i
      tmpscore = mmi(r[i], r[lmin_idx]) - l[i]
    else
      local ts2 = mmi(r[i], r[lmin_idx]) - l[i]
      if ts2 < tmpscore then
        rmax_idx = i
        tmpscore = ts2
      elseif ts2 == tmpscore then
        if r[rmax_idx] < r[i] then
          rmax_idx = i
          tmpscore = ts2
        end
      end
    end
  end
end
local lpoint, rpoint = r[lmin_idx] - l[lmin_idx] + 1, r[rmax_idx] - l[rmax_idx] + 1
local lp, rp = {}, {}
for i = 1, n do
  if i ~= rmax_idx and i ~= lmin_idx then
    table.insert(lp, mma(0, mmi(r[i], r[lmin_idx]) - l[i] + 1))
    table.insert(rp, mma(0, mmi(r[i], r[rmax_idx]) - mma(l[i], l[rmax_idx]) + 1))
  end
end
-- table.insert(lp, lpoint)
-- table.insert(rp, 0)
table.insert(lp, -1)
table.insert(rp, rpoint)
local t_idx = {}
for i = 1, n - 1 do
  t_idx[i] = i
end
table.sort(t_idx, function(x, y)
  if lp[x] == lp[y] then
    return rp[x] < rp[y]
  else
    return lp[x] < lp[y]
  end
end)
local inf = 1000000007
local st = SegTree.new(n - 1, function(x, y) return mmi(x, y) end, inf)
local ans = 0
for i = 1, n - 1 do
  -- print("ADD", i, t_idx[i], rp[t_idx[i]])
  st:setValue(i, rp[t_idx[i]])
  local lv = i == n - 1 and lpoint or lp[t_idx[i + 1]]
  local ret = mma(0, lv) + st.stage[1][1]
  -- print(i, mma(0, lv), st.stage[1][1])
  ans = mma(ans, ret)
end
print(ans)
