#include <bits/stdc++.h>
using namespace std;
template <class T>
ostream &operator<<(ostream &os, const vector<T> &p) {
  os << "[";
  for (auto &it : p) os << it << " ";
  return os << "]";
}
template <class S, class T>
ostream &operator<<(ostream &os, const pair<S, T> &p) {
  return os << "(" << p.first << "," << p.second << ")";
}
template <class T>
bool umin(T &a, T b) {
  return a > b ? (a = b, true) : false;
}
template <class T>
bool umax(T &a, T b) {
  return a < b ? (a = b, true) : false;
}
const int N = 2e5 + 10;
void solve() {
  int n;
  cin >> n;
  int q;
  cin >> q;
  vector<int> cols[n + 1];
  for (int i = 1; i <= q; i++) {
    int x, y;
    cin >> x >> y;
    for (int j = x; j <= y; j++) cols[j].push_back(i);
  }
  int sections = 0;
  for (int i = 1; i <= n; i++) sections += ((int)cols[i].size() > 0);
  int ans = 0;
  for (int i = 1; i <= q; i++) {
    int cur = sections;
    vector<int> del(q + 1);
    for (int j = 1; j <= n; j++) {
      if ((int)cols[j].size()) {
        if ((int)cols[j].size() == 1) {
          if (cols[j][0] == i)
            cur--;
          else
            del[cols[j][0]]++;
        } else if ((int)cols[j].size() == 2 &&
                   (cols[j][0] == i || cols[j][1] == i)) {
          if (cols[j][0] != i) del[cols[j][0]]++;
          if (cols[j][1] != i) del[cols[j][1]]++;
        }
      }
    }
    int mn = 1e7;
    for (int j = 1; j <= q; j++) {
      if (j != i) {
        umin(mn, del[j]);
      }
    }
    umax(ans, cur - mn);
  }
  cout << ans << endl;
}
signed main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  int q = 1;
  while (q--) solve();
  return 0;
}
