#include <bits/stdc++.h>
using namespace std;
struct edge {
  int to, flow, cap, cost, rev;
};
struct MinCostMaxFlow {
  int nodes;
  vector<int> prio, curflow, prevedge, prevnode, q, pot;
  vector<bool> inqueue;
  vector<vector<edge> > graph;
  MinCostMaxFlow() {}
  MinCostMaxFlow(int n)
      : nodes(n),
        prio(n, 0),
        curflow(n, 0),
        prevedge(n, 0),
        prevnode(n, 0),
        q(n, 0),
        pot(n, 0),
        inqueue(n, 0),
        graph(n) {}
  void addEdge(int source, int to, int capacity, int cost) {
    edge a = {to, 0, capacity, cost, (int)graph[to].size()};
    edge b = {source, 0, 0, -cost, (int)graph[source].size()};
    graph[source].push_back(a);
    graph[to].push_back(b);
  }
  void bellman_ford(int source, vector<int> &dist) {
    fill(dist.begin(), dist.end(), INT_MAX);
    dist[source] = 0;
    int qt = 0;
    q[qt++] = source;
    for (int qh = 0; (qh - qt) % nodes != 0; qh++) {
      int u = q[qh % nodes];
      inqueue[u] = false;
      for (auto &e : graph[u]) {
        if (e.flow >= e.cap) continue;
        int v = e.to;
        int newDist = dist[u] + e.cost;
        if (dist[v] > newDist) {
          dist[v] = newDist;
          if (!inqueue[v]) {
            inqueue[v] = true;
            q[qt++ % nodes] = v;
          }
        }
      }
    }
  }
  pair<int, int> minCostFlow(int source, int dest, int maxflow) {
    bellman_ford(source, pot);
    int flow = 0;
    int flow_cost = 0;
    while (flow < maxflow) {
      priority_queue<pair<int, int>, vector<pair<int, int> >,
                     greater<pair<int, int> > >
          q;
      q.push({0, source});
      fill(prio.begin(), prio.end(), INT_MAX);
      prio[source] = 0;
      curflow[source] = INT_MAX;
      while (!q.empty()) {
        int d = q.top().first;
        int u = q.top().second;
        q.pop();
        if (d != prio[u]) continue;
        for (int i = 0; i < graph[u].size(); i++) {
          edge &e = graph[u][i];
          int v = e.to;
          if (e.flow >= e.cap) continue;
          int newPrio = prio[u] + e.cost + pot[u] - pot[v];
          if (prio[v] > newPrio) {
            prio[v] = newPrio;
            q.push({newPrio, v});
            prevnode[v] = u;
            prevedge[v] = i;
            curflow[v] = min(curflow[u], e.cap - e.flow);
          }
        }
      }
      if (prio[dest] == INT_MAX) break;
      for (int i = 0; i < nodes; i++) pot[i] += prio[i];
      int df = min(curflow[dest], maxflow - flow);
      flow += df;
      for (int v = dest; v != source; v = prevnode[v]) {
        edge &e = graph[prevnode[v]][prevedge[v]];
        e.flow += df;
        graph[v][e.rev].flow -= df;
        flow_cost += df * e.cost;
      }
    }
    return {flow, flow_cost};
  }
};
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, q;
  cin >> n >> q;
  int mn[n + 1], mx[n + 1];
  for (int i = 1; i <= n; i++) {
    mn[i] = 1;
    mx[i] = n;
  }
  for (int i = 0; i < q; i++) {
    int t, l, r, v;
    cin >> t >> l >> r >> v;
    for (int j = l; j <= r; j++) {
      if (t == 1)
        mn[j] = max(mn[j], v);
      else
        mx[j] = min(mx[j], v);
    }
  }
  MinCostMaxFlow m(2 * n + 2);
  for (int i = 1; i <= n; i++) {
    m.addEdge(0, i, 1, 0);
    for (int j = mn[i]; j <= mx[i]; j++) m.addEdge(i, n + j, 1, 0);
    for (int j = 0; j < n; j++) m.addEdge(n + i, 2 * n + 1, 1, 2 * j + 1);
  }
  pair<int, int> g = m.minCostFlow(0, 2 * n + 1, n);
  if (g.first == n)
    cout << g.second << "\n";
  else
    cout << -1 << "\n";
}
