#include <bits/stdc++.h>
using namespace std;
template <typename _T>
inline void read(_T &f) {
  f = 0;
  _T fu = 1;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') fu = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    f = (f << 3) + (f << 1) + (c & 15);
    c = getchar();
  }
  f *= fu;
}
template <typename T>
void print(T x) {
  if (x < 0) putchar('-'), x = -x;
  if (x < 10)
    putchar(x + 48);
  else
    print(x / 10), putchar(x % 10 + 48);
}
template <typename T>
void print(T x, char t) {
  print(x);
  putchar(t);
}
template <typename T>
struct hash_map_t {
  vector<T> v, val, nxt;
  vector<int> head;
  int mod, tot, lastv;
  T lastans;
  bool have_ans;
  hash_map_t(int md = 0) {
    head.clear();
    v.clear();
    val.clear();
    nxt.clear();
    tot = 0;
    mod = md;
    nxt.resize(1);
    v.resize(1);
    val.resize(1);
    head.resize(mod);
    have_ans = 0;
  }
  void clear() { *this = hash_map_t(mod); }
  bool count(int x) {
    int u = x % mod;
    for (register int i = head[u]; i; i = nxt[i]) {
      if (v[i] == x) {
        have_ans = 1;
        lastv = x;
        lastans = val[i];
        return 1;
      }
    }
    return 0;
  }
  void ins(int x, int y) {
    int u = x % mod;
    nxt.push_back(head[u]);
    head[u] = ++tot;
    v.push_back(x);
    val.push_back(y);
  }
  int qry(int x) {
    if (have_ans && lastv == x) return lastans;
    count(x);
    return lastans;
  }
};
const int N = 205, M = 6e5 + 5, INF = 0x7fffffff;
struct edge_t {
  int u, v, next, cap, flow;
} G[M << 1];
int head[N], nowhead[N], d[N], x[N], y[N], _x[N], _y[N], a[N], b[N];
int n, m, s, t, tot = 1, al, bl;
inline void addedge(int u, int v, int cap) {
  G[++tot] = (edge_t){u, v, head[u], cap, 0}, head[u] = tot;
  G[++tot] = (edge_t){v, u, head[v], 0, 0}, head[v] = tot;
}
queue<int> q;
int bfs() {
  memset(d, 0, sizeof(d));
  d[s] = 1;
  q.push(s);
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (register int i = head[u]; i; i = G[i].next) {
      int v = G[i].v;
      if (!d[v] && G[i].cap > G[i].flow) {
        d[v] = d[u] + 1;
        q.push(v);
      }
    }
  }
  return d[t];
}
int dfs(int u, int Flow) {
  if (u == t || !Flow) return Flow;
  int flow = 0, f;
  for (register int &i = nowhead[u]; i; i = G[i].next) {
    int v = G[i].v;
    if (d[v] == d[u] + 1 && (f = dfs(v, min(Flow, G[i].cap - G[i].flow))) > 0) {
      G[i].flow += f;
      G[i ^ 1].flow -= f;
      Flow -= f;
      flow += f;
      if (!Flow) break;
    }
  }
  return flow;
}
int dinic() {
  int ans = 0;
  while (bfs()) {
    for (register int i = s; i <= t; i++) nowhead[i] = head[i];
    ans += dfs(s, INF);
  }
  return ans;
}
int main() {
  read(n);
  read(m);
  for (register int i = 1; i <= m; i++) {
    read(x[i]);
    read(y[i]);
    read(_x[i]);
    read(_y[i]);
    a[++al] = x[i];
    a[++al] = _x[i] + 1;
    b[++bl] = y[i];
    b[++bl] = _y[i] + 1;
  }
  sort(a + 1, a + al + 1);
  al = unique(a + 1, a + al + 1) - a - 1;
  sort(b + 1, b + bl + 1);
  bl = unique(b + 1, b + bl + 1) - b - 1;
  s = 0;
  t = al + bl + 1;
  for (register int i = 1; i < al; i++) addedge(s, i, a[i + 1] - a[i]);
  for (register int i = 1; i < bl; i++) addedge(i + al, t, b[i + 1] - b[i]);
  for (register int i = 1; i <= m; i++) {
    int xl = lower_bound(a + 1, a + al + 1, x[i]) - a;
    int xr = lower_bound(a + 1, a + al + 1, _x[i] + 1) - a;
    int yl = lower_bound(b + 1, b + bl + 1, y[i]) - b;
    int yr = lower_bound(b + 1, b + bl + 1, _y[i] + 1) - b;
    for (register int j = xl; j < xr; j++) {
      for (register int k = yl; k < yr; k++) {
        addedge(j, k + al, INF);
      }
    }
  }
  print(dinic(), '\n');
  return 0;
}
