Problem:
Score : 1000 points

Problem Statement

There are M chairs arranged in a line. The coordinate of the i-th chair (1 ≤ i ≤ M) is i.

N people of the Takahashi clan played too much games, and they are all suffering from backaches. They need to sit in chairs and rest, but they are particular about which chairs they sit in. Specifically, the i-th person wishes to sit in a chair whose coordinate is not greater than L_i, or not less than R_i. Naturally, only one person can sit in the same chair.

It may not be possible for all of them to sit in their favorite chairs, if nothing is done.
Aoki, who cares for the health of the people of the Takahashi clan, decides to provide additional chairs so that all of them can sit in chairs at their favorite positions.

Additional chairs can be placed at arbitrary real coordinates. Find the minimum required number of additional chairs.

Constraints

1 ≤ N,M ≤ 2 × 10^5

0 ≤ L_i < R_i ≤ M + 1(1 ≤ i ≤ N)

All input values are integers.

Input

Input is given from Standard Input in the following format:

N M
L_1 R_1
:
L_N R_N

Output

Print the minimum required number of additional chairs.

Sample Input 1

4 4
0 3
2 3
1 3
3 4

Sample Output 1

0

The four people can sit in chairs at the coordinates 3, 2, 1 and 4, respectively, and no more chair is needed.

Sample Input 2

7 6
0 7
1 5
3 6
2 7
1 6
2 6
3 7

Sample Output 2

2

If we place additional chairs at the coordinates 0 and 2.5, the seven people can sit at coordinates 0, 5, 3, 2, 6, 1 and 2.5, respectively.

Sample Input 3

3 1
1 2
1 2
1 2

Sample Output 3

2

Sample Input 4

6 6
1 6
1 6
1 5
1 5
2 6
2 6

Sample Output 4

2

Solution in Lua (LuaJIT 2.1.0) (judge verdict: Wrong Answer)

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

local AvlTree = {}
AvlTree.makenode = function(self, val, parent)
  local i = self.box[#self.box]
  if not i then i = #self.v + 1
  else table.remove(self.box)
  end
  self.v[i], self.p[i] = val, parent
  self.lc[i], self.rc[i], self.l[i], self.r[i] = 0, 0, 1, 1
  return i
end
AvlTree.create = function(self, lessthan, n)
  self.lessthan = lessthan
  self.root = 1
  self.box = {}
  for i = n + 1, 2, -1 do table.insert(self.box, i) end
  -- value, leftCount, rightCount, left, right, parent
  self.v, self.lc, self.rc, self.l, self.r, self.p = {}, {}, {}, {}, {}, {}
  for i = 1, n + 1 do
    self.v[i], self.p[i] = 0, 1
    self.lc[i], self.rc[i], self.l[i], self.r[i] = 0, 0, 1, 1
  end
end

AvlTree.recalc = function(self, i)
  local kl, kr = self.l[i], self.r[i]
  if 1 < kl then self.lc[i] = 1 + mma(self.lc[kl], self.rc[kl])
  else self.lc[i] = 0
  end
  if 1 < kr then self.rc[i] = 1 + mma(self.lc[kr], self.rc[kr])
  else self.rc[i] = 0
  end
end
AvlTree.recalcAll = function(self, i)
  while 1 < i do
    self:recalc(i)
    i = self.p[i]
  end
end

AvlTree.rotR = function(self, parent)
  local granp, child = self.p[parent], self.l[parent]
  self.r[child], self.l[parent] = parent, self.r[child]
  self.p[child], self.p[parent] = granp, child
  self.p[self.l[parent]] = parent
  if 1 < granp then
    if self.l[granp] == parent then
      self.l[granp] = child
    else
      self.r[granp] = child
    end
  else
    self.root = child
  end
end

AvlTree.rotL = function(self, parent)
  local granp, child = self.p[parent], self.r[parent]
  self.l[child], self.r[parent] = parent, self.l[child]
  self.p[child], self.p[parent] = granp, child
  self.p[self.r[parent]] = parent
  if 1 < granp then
    if self.r[granp] == parent then
      self.r[granp] = child
    else
      self.l[granp] = child
    end
  else
    self.root = child
  end
end

AvlTree.rotLR = function(self, lparent, rparent)
  local sp, sl, sr = self.p, self.l, self.r
  local granp, d = sp[rparent], sr[lparent]
  sp[lparent], sr[lparent] = d, sl[d]
  sp[rparent], sl[rparent] = d, sr[d]
  sp[sl[d]], sp[sr[d]] = lparent, rparent
  sp[d], sl[d], sr[d] = granp, lparent, rparent
  if 1 < granp then
    if sr[granp] == rparent then sr[granp] = d
    else sl[granp] = d
    end
  else self.root = d
  end
end

AvlTree.rotRL = function(self, rparent, lparent)
  local sp, sl, sr = self.p, self.l, self.r
  local granp, d = sp[lparent], sl[rparent]
  sp[rparent], sl[rparent] = d, sr[d]
  sp[lparent], sr[lparent] = d, sl[d]
  sp[sr[d]], sp[sl[d]] = rparent, lparent
  sp[d], sr[d], sl[d] = granp, rparent, lparent
  if 1 < granp then
    if sl[granp] == lparent then sl[granp] = d
    else sr[granp] = d
    end
  else self.root = d
  end
end

AvlTree.empty = function(self) return self.root <= 1 end

AvlTree.push = function(self, val)
  if self.root <= 1 then self.root = self:makenode(val, 1) return end
  local pos = self.root
  while true do
    if self.lessthan(val, self.v[pos]) then
      if 1 < self.l[pos] then
        pos = self.l[pos]
      else
        self.l[pos] = self:makenode(val, pos)
        pos = self.l[pos]
        break
      end
    else
      if 1 < self.r[pos] then
        pos = self.r[pos]
      else
        self.r[pos] = self:makenode(val, pos)
        pos = self.r[pos]
        break
      end
    end
  end
  while 1 < pos do
    local child, parent = pos, self.p[pos]
    if parent <= 1 then
      break
    end
    self:recalc(parent)
    local lcp_m_rcp = self.lc[parent] - self.rc[parent]
    if lcp_m_rcp % 2 ~= 0 then -- 1 or -1
      pos = parent
    elseif lcp_m_rcp == 2 then
      if self.lc[child] - 1 == self.rc[child] then
        self:rotR(parent)
        self:recalcAll(parent)
      else
        self:rotLR(child, parent)
        self:recalc(child)
        self:recalcAll(parent)
      end
      break
    elseif lcp_m_rcp == -2 then
      if self.rc[child] - 1 == self.lc[child] then
        self:rotL(parent)
        self:recalcAll(parent)
      else
        self:rotRL(child, parent)
        self:recalc(child)
        self:recalcAll(parent)
      end
      break
    else
      break
    end
  end
end

AvlTree.rmsub = function(self, node)
  while 1 < node do
    self:recalc(node)
    if self.lc[node] == self.rc[node] then
      node = self.p[node]
    elseif self.lc[node] + 1 == self.rc[node] then
      self:recalcAll(self.p[node])
      break
    else
      if self.lc[self.r[node]] == self.rc[self.r[node]] then
        self:rotL(node)
        self:recalcAll(node)
        break
      elseif self.lc[self.r[node]] + 1 == self.rc[self.r[node]] then
        local nr = self.r[node]
        self:rotL(node)
        self:recalc(node)
        node = nr
      else
        local nr = self.r[node]
        local nrl = self.l[nr]
        self:rotRL(nr, node)
        self:recalc(nr)
        self:recalc(node)
        node = nrl
      end
    end
  end
end

AvlTree.pop = function(self)
  local node = self.root
  while 1 < self.l[node] do
    node = self.l[node]
  end
  local v = self.v[node]
  local kp = self.p[node]
  self.p[self.r[node]] = kp
  if 1 < kp then
    self.l[kp] = self.r[node]
    self:rmsub(kp)
  else
    self.root = self.r[node]
  end
  table.insert(self.box, node)
  return v
end

AvlTree.new = function(lessthan, n)
  local obj = {}
  setmetatable(obj, {__index = AvlTree})
  obj:create(lessthan, n)
  return obj
end

local n, m = io.read("*n", "*n")
local ls, rs = {}, {}
local used = {}
local r_list = {}
local l_list = {}
for i = 1, m do
  r_list[i] = {}
  l_list[i] = {}
end
for i = 1, n do
  ls[i], rs[i] = io.read("*n", "*n")
  used[i] = false
  if rs[i] <= m then
    table.insert(r_list[rs[i]], i)
  end
  if 0 < ls[i] then
    table.insert(l_list[ls[i]], i)
  end
end
local function small_l_is_fast(a, b)
  return ls[a] < ls[b]
end
local avl1 = AvlTree.new(small_l_is_fast, 1)
local sit = 0
local chair_used = {}
for i = 1, m do
  for j = 1, #r_list[i] do
    avl1:push(r_list[i][j])
  end
  if not avl1:empty() then
    local top = avl1:pop()
    sit = sit + 1
    used[top] = true
    chair_used[i] = true
  else
    chair_used[i] = false
  end
end
local rem = 0
for i = m, 1, -1 do
  for j = 1, #l_list[i] do
    local v = l_list[i][j]
    if not used[v] then
      rem = rem + 1
    end
  end
  if 0 < rem and not chair_used[i] then
    sit = sit + 1
    rem = rem - 1
  end
end
print(n - sit)