//#define _GLIBCXX_DEBUG

#include<bits/stdc++.h>
using namespace std;

#define endl '\n'
#define lfs cout<<fixed<<setprecision(10)
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()
#define spa << " " <<
#define fi first
#define se second
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define EB emplace_back
#define rep(i,n,m) for(ll i = (n); i < (ll)(m); i++)
#define rrep(i,n,m) for(ll i = (ll)(m) - 1; i >= (ll)(n); i--)
using ll = long long;
using ld = long double;
const ll MOD1 = 1e9+7;
const ll MOD9 = 998244353;
const ll INF = 1e18;
using P = pair<ll, ll>;
template<typename T1, typename T2>
bool chmin(T1 &a,T2 b){if(a>b){a=b;return true;}else return false;}
template<typename T1, typename T2>
bool chmax(T1 &a,T2 b){if(a<b){a=b;return true;}else return false;}
ll median(ll a,ll b, ll c){return a+b+c-max({a,b,c})-min({a,b,c});}
void ans1(bool x){if(x) cout<<"Yes"<<endl;else cout<<"No"<<endl;}
void ans2(bool x){if(x) cout<<"YES"<<endl;else cout<<"NO"<<endl;}
void ans3(bool x){if(x) cout<<"Yay!"<<endl;else cout<<":("<<endl;}
template<typename T1,typename T2>
void ans(bool x,T1 y,T2 z){if(x)cout<<y<<endl;else cout<<z<<endl;}  
template<typename T>
void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++)
{cout<<v[i][0];for(ll j=1;j<w;j++)cout spa v[i][j];cout<<endl;}};
void debug(vector<string>&v,ll h,ll w){for(ll i=0;i<h;i++)
{for(ll j=0;j<w;j++)cout<<v[i][j];cout<<endl;}};
template<typename T>
void debug(vector<T>&v,ll n){if(n!=0)cout<<v[0];
for(ll i=1;i<n;i++)cout spa v[i];cout<<endl;};
template<typename T>
vector<vector<T>>vec(ll x, ll y, T w){
  vector<vector<T>>v(x,vector<T>(y,w));return v;}
ll gcd(ll x,ll y){ll r;while(y!=0&&(r=x%y)!=0){x=y;y=r;}return y==0?x:y;}
vector<ll>dx={1,-1,0,0,1,1,-1,-1};
vector<ll>dy={0,0,1,-1,1,-1,1,-1};
template<typename T>
vector<T> make_v(size_t a,T b){return vector<T>(a,b);}
template<typename... Ts>
auto make_v(size_t a,Ts... ts){
  return vector<decltype(make_v(ts...))>(a,make_v(ts...));
}
template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2>&p){
  return os << p.first << " " << p.second;
}
//mt19937 mt(chrono::steady_clock::now().time_since_epoch().count());
class Stack {
private:
  const int N, H;
  vector< int > node;
 
public:
  Stack(const int N, const int H) : N(N), H(H), node(N + H) { clear(); }
 
  inline bool empty(const int h) const { return node[N + h] == N + h; }
 
  inline int top(const int h) const { return node[N + h]; }
 
  inline void pop(const int h) { node[N + h] = node[node[N + h]]; }
 
  inline void push(const int h, const int u) { node[u] = node[N + h], node[N + h] = u; }
 
  inline void clear() { iota(node.begin() + N, node.end(), N); }
};
 
class List {
public:
  struct node {
    int prev, next;
  };
  const int N, H;
  vector< node > dat;
 
  List(const int N, const int H) : N(N), H(H), dat(N + H) { clear(); }
 
  inline bool empty(const int h) const { return (dat[N + h].next == N + h); }
 
  inline bool more_one(const int h) const { return dat[N + h].prev != dat[N + h].next; }
 
  inline void insert(const int h, const int u) {
    dat[u].prev = dat[N + h].prev, dat[u].next = N + h;
    dat[dat[N + h].prev].next = u, dat[N + h].prev = u;
  }
 
  inline void erase(const int u) {
    dat[dat[u].prev].next = dat[u].next, dat[dat[u].next].prev = dat[u].prev;
  }
 
  inline void clear() {
    for(int i = N; i < N + H; ++i) dat[i].prev = dat[i].next = i;
  }
};

template< typename flow_t >
struct PushRelabel {
  struct edge {
    int to;
    flow_t cap;
    int rev;
    bool isrev;
    int idx;
  };

  vector< vector< edge > > graph;
  vector< int > potential, cur_edge;
  vector< flow_t > ex;
  int V, height, relabels;
  List all_ver;
  Stack act_ver;

  PushRelabel(int V)
      : V(V), height(-1), relabels(0), ex(V, flow_t(0)), potential(V, 0), cur_edge(V), all_ver(V, V), act_ver(V, V), graph(V) {}

  void add_edge(int from, int to, flow_t cap, int idx = -1) {
    graph[from].emplace_back((edge) {to, cap, (int) graph[to].size(), false, idx});
    graph[to].emplace_back((edge) {from, 0, (int) graph[from].size() - 1, true, idx});
  }

  int calc_active(int t) {
    height = -1;
    for(int i = 0; i < V; i++) {
      if(potential[i] < V) {
        cur_edge[i] = 0;
        height = max(height, potential[i]);
        all_ver.insert(potential[i], i);
        if(ex[i] > 0 && i != t) act_ver.push(potential[i], i);
      } else {
        potential[i] = V + 1;
      }
    }
    return height;
  }

  void bfs(int t) {
    for(int i = 0; i < V; i++) {
      potential[i] = max(potential[i], V);
    }
    potential[t] = 0;
    queue< int > que;
    que.emplace(t);
    while(!que.empty()) {
      int p = que.front();
      que.pop();
      for(auto &e : graph[p]) {
        if(potential[e.to] == V && graph[e.to][e.rev].cap > 0) {
          potential[e.to] = potential[p] + 1;
          que.emplace(e.to);
        }
      }
    }
  }

  int init(int s, int t) {
    potential[s] = V + 1;
    bfs(t);
    for(auto &e : graph[s]) {
      if(potential[e.to] < V) {
        graph[e.to][e.rev].cap = e.cap;
        ex[s] -= e.cap;
        ex[e.to] += e.cap;
      }
      e.cap = 0;
    }
    return calc_active(t);
  }

  bool push(int u, int t, edge &e) {
    flow_t f = min(e.cap, ex[u]);
    int v = e.to;
    e.cap -= f, ex[u] -= f;
    graph[v][e.rev].cap += f, ex[v] += f;
    if(ex[v] == f && v != t) act_ver.push(potential[v], v);
    return ex[u] == 0;
  }

  int discharge(int u, int t) {
    for(int &i = cur_edge[u]; i < graph[u].size(); i++) {
      auto &e = graph[u][i];
      if(potential[u] == potential[e.to] + 1 && e.cap > 0) {
        if(push(u, t, e)) return potential[u];
      }
    }
    return relabel(u);
  }

  int global_relabel(int t) {
    bfs(t);
    all_ver.clear(), act_ver.clear();
    return calc_active(t);
  }

  void gap_relabel(const int u) {
    for(int i = potential[u]; i <= height; ++i) {
      for(int id = all_ver.dat[V + i].next; id < V; id = all_ver.dat[id].next) {
        potential[id] = V + 1;
      }
      all_ver.dat[V + i].prev = all_ver.dat[V + i].next = V + i;
    }
  }

  int relabel(const int u) {
    ++relabels;
    int prv = potential[u], cur = V;
    for(int i = 0; i < (int) graph[u].size(); ++i) {
      const edge &e = graph[u][i];
      if(cur > potential[e.to] + 1 && e.cap > 0) {
        cur_edge[u] = i;
        cur = potential[e.to] + 1;
      }
    }
    if(all_ver.more_one(prv)) {
      all_ver.erase(u);
      if((potential[u] = cur) == V) return potential[u] = V + 1, prv;
      act_ver.push(cur, u);
      all_ver.insert(cur, u);
      height = max(height, cur);
    } else {
      gap_relabel(u);
      return height = prv - 1;
    }
    return cur;
  }

  flow_t max_flow(int s, int t) {
    int level = init(s, t);
    while(level >= 0) {
      if(act_ver.empty(level)) {
        --level;
        continue;
      }
      int u = act_ver.top(level);
      act_ver.pop(level);
      level = discharge(u, t);
      if(relabels * 2 >= V) {
        level = global_relabel(t);
        relabels = 0;
      }
    }
    return ex[t];
  }
};


int main(){
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  ll res=0,buf=0;
  bool judge = true;
  ll n,m;cin>>n>>m;
  //1~M:L Mから初めて左へ
  //M+1~2M:M+1から初めて右へ
  //0:M,M+1に辺を張る
  //2M+1~2*M+N:頂点担当
  //2*M+N+1:goal
  PushRelabel<int>dinic(3*m+n+2);
  rep(i,1,m)dinic.add_edge(i+1,i,n);
  rep(i,m+1,2*m)dinic.add_edge(i,i+1,n);
  rep(i,1,m+1){
    dinic.add_edge(i,2*m+i,1);
    dinic.add_edge(m+i,2*m+i,1);
    dinic.add_edge(2*m+i,3*m+n+1,1);
  }
  rep(i,3*m+1,3*m+n+1){
    ll l,r;cin>>l>>r;
    dinic.add_edge(0,i,1);
    if(l>=1)dinic.add_edge(i,l,1);
    if(r<=m)dinic.add_edge(i,m+r,1);
  }
  ll mx=dinic.max_flow(0,3*m+n+1);
  //dinic.output();
  //cout<<mx<<endl;
  cout<<n-mx<<endl;
  return 0;
}