Problem: Oleg the bank client solves an interesting chess problem: place on n × n chessboard the maximum number of rooks so that they don't beat each other. Of course, no two rooks can share the same cell.

Remind that a rook standing in the cell (a, b) beats a rook standing in the cell (x, y) if and only if a = x or b = y.

Unfortunately (of fortunately?) for Oleg the answer in this problem was always n, so the task bored Oleg soon. He decided to make it more difficult by removing some cells from the board. If a cell is deleted, Oleg can't put a rook there, but rooks do beat each other "through" deleted cells.

Oleg deletes the cells in groups, namely, he repeatedly choose a rectangle with sides parallel to the board sides and deletes all the cells inside the rectangle. Formally, if he chooses a rectangle, lower left cell of which has coordinates (x1, y1), and upper right cell of which has coordinates (x2, y2), then he deletes all such cells with coordinates (x, y) that x1 ≤ x ≤ x2 and y1 ≤ y ≤ y2. It is guaranteed that no cell is deleted twice, i.e. the chosen rectangles do not intersect.

This version of the problem Oleg can't solve, and his friend Igor is busy at a conference, so he can't help Oleg.

You are the last hope for Oleg! Help him: given the size of the board and the deleted rectangles find the maximum possible number of rooks that could be placed on the board so that no two rooks beat each other.

Input

The first line contains single integer n (1 ≤ n ≤ 10000) — the size of the board.

The second line contains single integer q (0 ≤ q ≤ 10000) — the number of deleted rectangles.

The next q lines contain the information about the deleted rectangles.

Each of these lines contains four integers x1, y1, x2 and y2 (1 ≤ x1 ≤ x2 ≤ n, 1 ≤ y1 ≤ y2 ≤ n) — the coordinates of the lower left and the upper right cells of a deleted rectangle.

If is guaranteed that the rectangles do not intersect.

Output

In the only line print the maximum number of rooks Oleg can place on the board so that no two rooks beat each other.

Examples

Input

5
5
1 1 2 1
1 3 1 5
4 1 5 5
2 5 2 5
3 2 3 5


Output

3


Input

8
4
2 2 4 6
1 8 1 8
7 1 8 2
5 4 6 8


Output

8

Note

Here is the board and the example of rooks placement in the first example:

<image>

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr), ios::sync_with_stdio(false),
        cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T, typename V>
void ndarray(vector<T> &vec, const V &val, int len) {
  vec.assign(len, val);
}
template <typename T, typename V, typename... Args>
void ndarray(vector<T> &vec, const V &val, int len, Args... args) {
  vec.resize(len),
      for_each(begin(vec), end(vec), [&](T &v) { ndarray(v, val, args...); });
}
template <typename T>
bool chmax(T &m, const T q) {
  if (m < q) {
    m = q;
    return true;
  } else
    return false;
}
template <typename T>
bool chmin(T &m, const T q) {
  if (m > q) {
    m = q;
    return true;
  } else
    return false;
}
int floor_lg(long long x) { return x <= 0 ? -1 : 63 - __builtin_clzll(x); }
template <typename T1, typename T2>
pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) {
  return make_pair(l.first + r.first, l.second + r.second);
}
template <typename T1, typename T2>
pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) {
  return make_pair(l.first - r.first, l.second - r.second);
}
template <typename T>
vector<T> sort_unique(vector<T> vec) {
  sort(vec.begin(), vec.end()),
      vec.erase(unique(vec.begin(), vec.end()), vec.end());
  return vec;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
  for (auto &v : vec) is >> v;
  return is;
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << '[';
  for (auto v : vec) os << v << ',';
  os << ']';
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const deque<T> &vec) {
  os << "deq[";
  for (auto v : vec) os << v << ',';
  os << ']';
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const set<T> &vec) {
  os << '{';
  for (auto v : vec) os << v << ',';
  os << '}';
  return os;
}
template <typename T, typename TH>
ostream &operator<<(ostream &os, const unordered_set<T, TH> &vec) {
  os << '{';
  for (auto v : vec) os << v << ',';
  os << '}';
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const multiset<T> &vec) {
  os << '{';
  for (auto v : vec) os << v << ',';
  os << '}';
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const unordered_multiset<T> &vec) {
  os << '{';
  for (auto v : vec) os << v << ',';
  os << '}';
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &pa) {
  os << '(' << pa.first << ',' << pa.second << ')';
  return os;
}
template <typename TK, typename TV>
ostream &operator<<(ostream &os, const map<TK, TV> &mp) {
  os << '{';
  for (auto v : mp) os << v.first << "=>" << v.second << ',';
  os << '}';
  return os;
}
template <typename TK, typename TV, typename TH>
ostream &operator<<(ostream &os, const unordered_map<TK, TV, TH> &mp) {
  os << '{';
  for (auto v : mp) os << v.first << "=>" << v.second << ',';
  os << '}';
  return os;
}
template <class Cap>
struct mf_graph {
  struct simple_queue_int {
    std::vector<int> payload;
    int pos = 0;
    void reserve(int n) { payload.reserve(n); }
    int size() const { return int(payload.size()) - pos; }
    bool empty() const { return pos == int(payload.size()); }
    void push(const int &t) { payload.push_back(t); }
    int &front() { return payload[pos]; }
    void clear() {
      payload.clear();
      pos = 0;
    }
    void pop() { pos++; }
  };
  mf_graph() : _n(0) {}
  mf_graph(int n) : _n(n), g(n) {}
  int add_edge(int from, int to, Cap cap) {
    assert(0 <= from && from < _n);
    assert(0 <= to && to < _n);
    assert(0 <= cap);
    int m = int(pos.size());
    pos.push_back({from, int(g[from].size())});
    int from_id = int(g[from].size());
    int to_id = int(g[to].size());
    if (from == to) to_id++;
    g[from].push_back(_edge{to, to_id, cap});
    g[to].push_back(_edge{from, from_id, 0});
    return m;
  }
  struct edge {
    int from, to;
    Cap cap, flow;
  };
  edge get_edge(int i) {
    int m = int(pos.size());
    assert(0 <= i && i < m);
    auto _e = g[pos[i].first][pos[i].second];
    auto _re = g[_e.to][_e.rev];
    return edge{pos[i].first, _e.to, _e.cap + _re.cap, _re.cap};
  }
  std::vector<edge> edges() {
    int m = int(pos.size());
    std::vector<edge> result;
    for (int i = 0; i < m; i++) {
      result.push_back(get_edge(i));
    }
    return result;
  }
  void change_edge(int i, Cap new_cap, Cap new_flow) {
    int m = int(pos.size());
    assert(0 <= i && i < m);
    assert(0 <= new_flow && new_flow <= new_cap);
    auto &_e = g[pos[i].first][pos[i].second];
    auto &_re = g[_e.to][_e.rev];
    _e.cap = new_cap - new_flow;
    _re.cap = new_flow;
  }
  std::vector<int> level, iter;
  simple_queue_int que;
  void _bfs(int s, int t) {
    std::fill(level.begin(), level.end(), -1);
    level[s] = 0;
    que.clear();
    que.push(s);
    while (!que.empty()) {
      int v = que.front();
      que.pop();
      for (auto e : g[v]) {
        if (e.cap == 0 || level[e.to] >= 0) continue;
        level[e.to] = level[v] + 1;
        if (e.to == t) return;
        que.push(e.to);
      }
    }
  }
  Cap _dfs(int v, int s, Cap up) {
    if (v == s) return up;
    Cap res = 0;
    int level_v = level[v];
    for (int &i = iter[v]; i < int(g[v].size()); i++) {
      _edge &e = g[v][i];
      if (level_v <= level[e.to] || g[e.to][e.rev].cap == 0) continue;
      Cap d = _dfs(e.to, s, std::min(up - res, g[e.to][e.rev].cap));
      if (d <= 0) continue;
      g[v][i].cap += d;
      g[e.to][e.rev].cap -= d;
      res += d;
      if (res == up) return res;
    }
    level[v] = _n;
    return res;
  }
  Cap flow(int s, int t) { return flow(s, t, std::numeric_limits<Cap>::max()); }
  Cap flow(int s, int t, Cap flow_limit) {
    assert(0 <= s && s < _n);
    assert(0 <= t && t < _n);
    assert(s != t);
    level.assign(_n, 0), iter.assign(_n, 0);
    que.clear();
    Cap flow = 0;
    while (flow < flow_limit) {
      _bfs(s, t);
      if (level[t] == -1) break;
      std::fill(iter.begin(), iter.end(), 0);
      Cap f = _dfs(t, s, flow_limit - flow);
      if (!f) break;
      flow += f;
    }
    return flow;
  }
  std::vector<bool> min_cut(int s) {
    std::vector<bool> visited(_n);
    simple_queue_int que;
    que.push(s);
    while (!que.empty()) {
      int p = que.front();
      que.pop();
      visited[p] = true;
      for (auto e : g[p]) {
        if (e.cap && !visited[e.to]) {
          visited[e.to] = true;
          que.push(e.to);
        }
      }
    }
    return visited;
  }
  int _n;
  struct _edge {
    int to, rev;
    Cap cap;
  };
  std::vector<std::pair<int, int>> pos;
  std::vector<std::vector<_edge>> g;
};
std::vector<int> nonrecursive_segtree_points(int N, int l, int r) {
  std::vector<int> ret;
  l += N, r += N;
  while (l < r) {
    if (l & 1) ret.push_back(l++);
    if (r & 1) ret.push_back(--r);
    l >>= 1, r >>= 1;
  }
  std::sort(ret.begin(), ret.end());
  return ret;
}
int main() {
  int N, Q;
  cin >> N >> Q;
  vector<vector<pair<bool, pint>>> x2yy(N + 1);
  map<int, pint> mp;
  mp[0] = pint(N, 0);
  x2yy[N].emplace_back(1, pint(0, N));
  while (Q--) {
    int x1, y1, x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    x1--, y1--;
    x2yy[x1].emplace_back(1, pint(y1, y2));
    x2yy[x2].emplace_back(0, pint(y1, y2));
  }
  for (auto &vec : x2yy) sort(vec.begin(), vec.end());
  {};
  vector<vector<int>> recs;
  auto add_rect = [&](const vector<int> &v) {
    if (v[0] < v[1]) recs.emplace_back(v);
  };
  for (int i = (0), i_end_ = (N + 1); i < i_end_; i++) {
    for (auto [m, p] : x2yy[i]) {
      if (m == 1) {
        auto itr = prev(mp.upper_bound(p.first));
        int l = itr->first, r = itr->second.first, j = itr->second.second;
        add_rect({j, i, l, r});
        mp.erase(l);
        if (l < p.first) mp[l] = pint(p.first, i);
        if (p.second < r) mp[p.second] = pint(r, i);
      } else {
        auto itr = mp.lower_bound(p.first);
        if (itr != mp.begin()) {
          itr--;
          if (itr->second.first == p.first) {
            add_rect({itr->second.second, i, itr->first, itr->second.first});
            p.first = itr->first;
            mp.erase(itr->first);
          }
        }
        itr = mp.lower_bound(p.first);
        if (itr != mp.end() and itr->first == p.second) {
          add_rect({itr->second.second, i, itr->first, itr->second.first});
          p.second = itr->second.first;
          mp.erase(itr);
        }
        mp[p.first] = pint(p.second, i);
      }
      {};
    }
  }
  {};
  mf_graph<int> maxflow(4 * N + 2 + recs.size());
  const int s_mf = 4 * N, t_mf = s_mf + 1;
  for (int i = (0), i_end_ = (N); i < i_end_; i++) {
    maxflow.add_edge(s_mf, N + i, 1);
    maxflow.add_edge(N * 3 + i, t_mf, 1);
  }
  for (int i = (1), i_end_ = (N); i < i_end_; i++) {
    maxflow.add_edge(i * 2, i, N);
    maxflow.add_edge(i * 2 + 1, i, N);
    maxflow.add_edge(i + 2 * N, i * 2 + 2 * N, N);
    maxflow.add_edge(i + 2 * N, i * 2 + 1 + 2 * N, N);
  }
  for (int q = (0), q_end_ = (recs.size()); q < q_end_; q++) {
    for (auto i : nonrecursive_segtree_points(N, recs[q][0], recs[q][1])) {
      maxflow.add_edge(i, t_mf + 1 + q, N);
    }
    for (auto i : nonrecursive_segtree_points(N, recs[q][2], recs[q][3])) {
      maxflow.add_edge(t_mf + 1 + q, i + 2 * N, N);
    }
  }
  cout << maxflow.flow(s_mf, t_mf) << '\n';
}