func_code_string: #include <bits/stdc++.h>   using namespace std;   struct Dinic {     static const int MXN = (int)2e6;     struct Edge {       int v, f, re;     };     int n, s, t, level[MXN];     vector<Edge> E[MXN];     void init(int _n, int _s, int _t) {       n = _n;       s = _s;       t = _t;     }     void add_edge(int u, int v, int f) {       E[u].push_back({v, f, (int)E[v].size()});       E[v].push_back({u, 0, (int)E[u].size() - 1});     }     bool BFS() {       for (int i = 0; i < n; i++) level[i] = -1;       queue<int> que;       que.push(s);       level[s] = 0;       while (!que.empty()) {         int u = que.front();         que.pop();         for (auto &it : E[u]) {           if (it.f > 0 && level[it.v] == -1) {             level[it.v] = level[u] + 1;             que.push(it.v);           }         }       }       return level[t] != -1;     }     int DFS(int u, int nf) {       if (u == t) return nf;       int res = 0;       for (auto &it : E[u]) {         if (it.f > 0 && level[it.v] == level[u] + 1) {           int tf = DFS(it.v, min(nf, it.f));           res += tf;           nf -= tf;           it.f -= tf;           E[it.v][it.re].f += tf;           if (nf == 0) return res;         }       }       if (!res) level[u] = -1;       return res;     }     int flow(int res = 0) {       while (BFS()) res += DFS(s, 2147483647);       return res;     }   } flow;   struct Node {     int l, r, y, v;     bool operator<(const Node &rhs) const { return y < rhs.y; }   };   int n, q, s, t, tot;   vector<Node> seg;   namespace segtree {   static const int N = (int)1e4 + 5;   static const int inf = (int)1e9;   int id[N * 4], id2[N * 4], tag[N * 4];   void pull(int o, int lson, int rson) {     id[o] = tot++;     if (!tag[lson]) flow.add_edge(id[o], id[lson], inf);     if (!tag[rson]) flow.add_edge(id[o], id[rson], inf);   }   void build1(int l, int r, int o = 0) {     if (l + 1 == r) return void(id[o] = n + l);     int mid = (l + r) >> 1, lson = o * 2 + 1, rson = o * 2 + 2;     build1(l, mid, lson);     build1(mid, r, rson);     pull(o, lson, rson);   }   void build2(int l, int r, int o = 0) {     if (l + 1 == r) return void(id2[o] = l);     int mid = (l + r) >> 1, lson = o * 2 + 1, rson = o * 2 + 2;     id2[o] = tot++;     build2(l, mid, lson);     build2(mid, r, rson);     flow.add_edge(id2[lson], id2[o], inf);     flow.add_edge(id2[rson], id2[o], inf);   }   void build(int l, int r) {     build1(l, r);     build2(l, r);   }   void modify1(int l, int r, int ql, int qr, int v, int o = 0) {     if (ql <= l && r <= qr) return void(tag[o] += v);     int mid = (l + r) >> 1, lson = o * 2 + 1, rson = o * 2 + 2;     if (ql < mid) modify1(l, mid, ql, qr, v, lson);     if (mid < qr) modify1(mid, r, ql, qr, v, rson);     pull(o, lson, rson);   }   void modify2(int l, int r, int ql, int qr, int o = 0) {     if (ql <= l && r <= qr) return void(flow.add_edge(id2[o], id[0], inf));     int mid = (l + r) >> 1, lson = o * 2 + 1, rson = o * 2 + 2;     if (ql < mid) modify2(l, mid, ql, qr, lson);     if (mid < qr) modify2(mid, r, ql, qr, rson);   }   void modify(int l, int r, int ql1, int qr1, int v, int ql2, int qr2) {     if (!tag[0] && ql2 < qr2) modify2(l, r, ql2, qr2);     modify1(l, r, ql1, qr1, v);   }   }  // namespace segtree   void init() {     cin >> n >> q;     for (int i = 0; i < q; ++i) {       int x1, y1, x2, y2;       cin >> x1 >> y1 >> x2 >> y2;       seg.push_back({x1, x2 + 1, y1, 1});       seg.push_back({x1, x2 + 1, y2 + 1, -1});     }     sort(seg.begin(), seg.end());   }   void solve() {     tot = 2 * n + 2, s = 0, t = 2 * n + 1;     for (int i = 1; i <= n; ++i) {       flow.add_edge(s, i, 1);       flow.add_edge(i + n, t, 1);     }     segtree::build(1, n + 1);     int preY = 1;     for (auto [l, r, y, v] : seg) {       segtree::modify(1, n + 1, l, r, v, preY, y);       preY = y;     }     if (preY < n + 1) segtree::modify2(1, n + 1, preY, n + 1);     flow.init(tot, s, t);     cout << flow.flow() <<   n ;   }   int main() {     ios_base::sync_with_stdio(0), cin.tie(0);     init();     solve();   }   