#include <bits/stdc++.h>
long long dx[8] = {0, 1, 0, -1, 1, 1, -1, -1};
long long dy[8] = {1, 0, -1, 0, -1, 1, 1, -1};
using namespace std;
class pa3 {
 public:
  long long x;
  long long y, z;
  pa3(long long x = 0, long long y = 0, long long z = 0) : x(x), y(y), z(z) {}
  bool operator<(const pa3 &p) const {
    if (x != p.x) return x < p.x;
    if (y != p.y) return y < p.y;
    return z < p.z;
  }
  bool operator>(const pa3 &p) const {
    if (x != p.x) return x > p.x;
    if (y != p.y) return y > p.y;
    return z > p.z;
  }
  bool operator==(const pa3 &p) const {
    return x == p.x && y == p.y && z == p.z;
  }
  bool operator!=(const pa3 &p) const {
    return !(x == p.x && y == p.y && z == p.z);
  }
};
class pa4 {
 public:
  long long x;
  long long y, z, w;
  pa4(long long x = 0, long long y = 0, long long z = 0, long long w = 0)
      : x(x), y(y), z(z), w(w) {}
  bool operator<(const pa4 &p) const {
    if (x != p.x) return x < p.x;
    if (y != p.y) return y < p.y;
    if (z != p.z) return z < p.z;
    return w < p.w;
  }
  bool operator>(const pa4 &p) const {
    if (x != p.x) return x > p.x;
    if (y != p.y) return y > p.y;
    if (z != p.z) return z > p.z;
    return w > p.w;
  }
  bool operator==(const pa4 &p) const {
    return x == p.x && y == p.y && z == p.z && w == p.w;
  }
};
class pa2 {
 public:
  long long x, y;
  pa2(long long x = 0, long long y = 0) : x(x), y(y) {}
  pa2 operator+(pa2 p) { return pa2(x + p.x, y + p.y); }
  pa2 operator-(pa2 p) { return pa2(x - p.x, y - p.y); }
  bool operator<(const pa2 &p) const { return y != p.y ? y < p.y : x < p.x; }
  bool operator>(const pa2 &p) const { return x != p.x ? x < p.x : y < p.y; }
  bool operator==(const pa2 &p) const {
    return abs(x - p.x) == 0 && abs(y - p.y) == 0;
  }
  bool operator!=(const pa2 &p) const {
    return !(abs(x - p.x) == 0 && abs(y - p.y) == 0);
  }
};
string itos(long long i) {
  ostringstream s;
  s << i;
  return s.str();
}
long long gcd(long long v, long long b) {
  if (v > b) return gcd(b, v);
  if (v == b) return b;
  if (b % v == 0) return v;
  return gcd(v, b % v);
}
long long mod;
long long extgcd(long long a, long long b, long long &x, long long &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  long long d = extgcd(b, a % b, y, x);
  y -= a / b * x;
  return d;
}
pair<long long, long long> operator+(const pair<long long, long long> &l,
                                     const pair<long long, long long> &r) {
  return {l.first + r.first, l.second + r.second};
}
pair<long long, long long> operator-(const pair<long long, long long> &l,
                                     const pair<long long, long long> &r) {
  return {l.first - r.first, l.second - r.second};
}
long long pr[1001010];
long long inv[1001010];
long long beki(long long wa, long long rr, long long warukazu) {
  if (rr == 0) return 1 % warukazu;
  if (rr == 1) return wa % warukazu;
  wa %= warukazu;
  if (rr % 2 == 1)
    return ((long long)beki(wa, rr - 1, warukazu) * (long long)wa) % warukazu;
  long long zx = beki(wa, rr / 2, warukazu);
  return (zx * zx) % warukazu;
}
long long comb(long long nn, long long rr) {
  if (rr < 0 || rr > nn || nn < 0) return 0;
  long long r = pr[nn] * inv[rr];
  r %= mod;
  r *= inv[nn - rr];
  r %= mod;
  return r;
}
void gya(long long ert) {
  pr[0] = 1;
  for (long long i = 1; i <= ert; i++) {
    pr[i] = (pr[i - 1] * i) % mod;
  }
  inv[ert] = beki(pr[ert], mod - 2, mod);
  for (long long i = ert - 1; i >= 0; i--) {
    inv[i] = inv[i + 1] * (i + 1) % mod;
  }
}
struct edge {
  long long to, cap, num, moto;
};
vector<edge> ZANYO[100020];
long long label[100020];
queue<pair<long long, long long> > qu_bfs;
long long dokomade[100020];
void add_edge(long long s_point, long long t_point, long long capa) {
  ZANYO[s_point].push_back(
      (edge){t_point, capa, (long long)ZANYO[t_point].size(), 0});
  ZANYO[t_point].push_back(
      (edge){s_point, 0, (long long)ZANYO[s_point].size() - 1, 1});
}
void bfs_dinic(long long s_point, long long N) {
  for (long long i = 0; i < N; i++) label[i] = -1;
  while (qu_bfs.size()) qu_bfs.pop();
  qu_bfs.push(make_pair(s_point, 0));
  while (qu_bfs.size()) {
    pair<long long, long long> z = qu_bfs.front();
    qu_bfs.pop();
    if (label[z.first] >= 0) continue;
    label[z.first] = z.second;
    for (auto &v : ZANYO[z.first]) {
      if (v.cap == 0) continue;
      if (v.cap < 0) {
        cout << "error" << endl;
        exit(0);
      }
      if (label[v.to] >= 0) continue;
      qu_bfs.push(make_pair(v.to, z.second + 1));
    }
  }
  return;
}
long long dfs_dinic(long long s_point, long long t_point, long long ima_flow) {
  if (s_point == t_point) return ima_flow;
  while (1) {
    if (dokomade[s_point] >= ZANYO[s_point].size()) break;
    long long edanum = dokomade[s_point];
    if (ZANYO[s_point][edanum].cap < 0) {
      cout << "minus" << endl;
      exit(0);
    }
    if (ZANYO[s_point][edanum].cap <= 0 ||
        label[s_point] + 1 != label[ZANYO[s_point][edanum].to]) {
      dokomade[s_point]++;
      continue;
    }
    long long W = dfs_dinic(ZANYO[s_point][edanum].to, t_point,
                            min(ZANYO[s_point][edanum].cap, ima_flow));
    if (W > 0) {
      ZANYO[s_point][edanum].cap -= W;
      ZANYO[ZANYO[s_point][edanum].to][ZANYO[s_point][edanum].num].cap += W;
      return W;
    }
    dokomade[s_point]++;
  }
  return 0;
}
long long max_flow_dinic(long long s_point, long long t_point, long long N) {
  long long jougen = 1000000007 * 1000000000ll;
  long long ans_flow = 0;
  while (1) {
    bfs_dinic(s_point, N);
    if (label[t_point] == -1) break;
    for (long long i = 0; i < N; i++) dokomade[i] = 0;
    while (1) {
      long long ima_flow = dfs_dinic(s_point, t_point, jougen + 1);
      if (ima_flow == 0) break;
      ans_flow += ima_flow;
    }
  }
  return ans_flow;
}
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  vector<pa4> ve;
  long long n, q;
  cin >> n >> q;
  set<long long> sex, sey;
  sex.insert(0);
  sex.insert(n);
  sey.insert(0);
  sey.insert(n);
  for (long long i = 0; i < q; i++) {
    long long x1, y1, x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    x1--, y1--;
    sex.insert(x1);
    sex.insert(x2);
    sey.insert(y1);
    sey.insert(y2);
    ve.push_back((pa4){x1, x2, y1, y2});
  }
  vector<long long> vx, vy;
  for (auto it = sex.begin(); it != sex.end(); it++) vx.push_back(*it);
  for (auto it = sey.begin(); it != sey.end(); it++) vy.push_back(*it);
  long long a = vx.size() - 1;
  long long b = vy.size() - 1;
  set<pair<long long, long long> > se;
  for (long long i = 0; i < a; i++)
    for (long long j = 0; j < b; j++) {
      long long sx = vx[i], sy = vx[i + 1];
      long long tx = vy[j], ty = vy[j + 1];
      bool bo = 0;
      for (auto v : ve) {
        if (sx >= v.x && v.y >= sy && tx >= v.z && v.w >= ty) bo = 1;
      }
      if (bo) se.insert(make_pair(i, j));
    }
  long long A[200], B[200];
  for (long long i = 0; i < a; i++) {
    long long sx = vx[i], sy = vx[i + 1];
    add_edge(0, 1 + i, sy - sx);
    A[i] = sy - sx;
  }
  for (long long j = 0; j < b; j++) {
    long long tx = vy[j], ty = vy[j + 1];
    add_edge(a + 1 + j, a + b + 1, ty - tx);
    B[j] = ty - tx;
  }
  for (auto it = se.begin(); it != se.end(); it++) {
    pair<long long, long long> z = *it;
    add_edge(1 + z.first, a + 1 + z.second, min(A[z.first], B[z.second]));
  }
  cout << max_flow_dinic(0, a + b + 1, a + b + 5) << endl;
  return 0;
}
