#include <bits/stdc++.h>
using namespace std;
const int INF = 2e9;
const int MAXN = 900;
const int MAXM = 1900000;
int N, edges;
int last[MAXN], preve[MAXM], head[MAXM];
int Cap[MAXM], Flow[MAXM];
int dist[MAXN];
int nextEdge[MAXN];
queue<int> Q;
void init(int N) {
  edges = 0;
  memset(last, -1, sizeof last);
}
set<int> namex, namey;
vector<int> xx, yy;
void handlex(int f) {
  if (namex.find(f) != namex.end()) return;
  namex.insert(f);
  xx.push_back(f);
}
void handley(int f) {
  if (namey.find(f) != namey.end()) return;
  yy.push_back(f);
  namey.insert(f);
}
inline void add_edge(int u, int v, int cap, int flow = 0) {
  head[edges] = v;
  preve[edges] = last[u];
  Cap[edges] = cap;
  Flow[edges] = flow;
  last[u] = edges++;
  head[edges] = u;
  preve[edges] = last[v];
  Cap[edges] = 0;
  Flow[edges] = 0;
  last[v] = edges++;
}
inline bool dinicBfs(int S, int E, int N) {
  int from = S, to, cap, flow;
  memset(dist, 0, sizeof(int) * N);
  dist[from] = 1;
  while (!Q.empty()) Q.pop();
  Q.push(from);
  while (!Q.empty()) {
    from = Q.front();
    Q.pop();
    for (int e = last[from]; e >= 0; e = preve[e]) {
      to = head[e];
      cap = Cap[e];
      flow = Flow[e];
      if (!dist[to] && cap > flow) {
        dist[to] = dist[from] + 1;
        Q.push(to);
        if (to == E) return true;
      }
    }
  }
  return (dist[E] != 0);
}
inline int dfs(int from, int minEdge, int E) {
  if (!minEdge) return 0;
  if (from == E) return minEdge;
  int to, e, cap, flow, ret;
  for (; nextEdge[from] >= 0; nextEdge[from] = preve[e]) {
    e = nextEdge[from];
    to = head[e];
    cap = Cap[e];
    flow = Flow[e];
    if (dist[to] != dist[from] + 1) continue;
    ret = dfs(to, min(minEdge, cap - flow), E);
    if (ret) {
      Flow[e] += ret;
      Flow[e ^ 1] -= ret;
      return ret;
    }
  }
  return 0;
}
int dinicUpdate(int S, int E) {
  int flow = 0;
  while (int minEdge = dfs(S, INF, E)) {
    if (minEdge == 0) break;
    flow += minEdge;
  }
  return flow;
}
int maxFlow(int S, int E, int N) {
  int totFlow = 0;
  while (dinicBfs(S, E, N)) {
    for (int i = 0; i <= N; i++) nextEdge[i] = last[i];
    totFlow += dinicUpdate(S, E);
  }
  return totFlow;
}
int x1[60], y11[60], x2[60], y2[60];
int main() {
  int i, j, k, l, m, n;
  init(32);
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= m; i++) {
    scanf("%d%d%d%d", &x1[i], &y11[i], &x2[i], &y2[i]);
    x2[i]++;
    y2[i]++;
    handlex(x1[i]);
    handlex(x2[i]);
    handley(y11[i]);
    handley(y2[i]);
  }
  sort(xx.begin(), xx.end());
  sort(yy.begin(), yy.end());
  int so = xx.size() + yy.size() + 1;
  int sink = so + 1;
  for (int i = 1; i <= m; i++) {
    for (int j = 1; j < xx.size(); j++) {
      if (xx[j] <= x1[i]) continue;
      if (xx[j] > x2[i]) break;
      for (int k = 1; k < yy.size(); k++) {
        if (yy[k] <= y11[i]) continue;
        if (yy[k] > y2[i]) break;
        int g = xx.size() + k;
        add_edge(j, g, INF);
      }
    }
  }
  for (int i = 1; i < xx.size(); i++) {
    add_edge(so, i, xx[i] - xx[i - 1]);
  }
  for (int i = 1; i < yy.size(); i++) {
    int g = xx.size() + i;
    add_edge(g, sink, yy[i] - yy[i - 1]);
  }
  int ans = maxFlow(so, sink, sink + 2);
  cout << ans << endl;
}
