func_code_string: #include <bits/stdc++.h>   using namespace std;   const int mod = 1e9 + 7;   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     ;     int n, q, i, j, l, r;     cin >> n >> q;     int auxi[n + 2], sum[n + 2];     memset(auxi, 0, sizeof(auxi));     memset(sum, 0, sizeof(sum));     vector<pair<int, int> > v;     for (i = 0; i < q; i++) {       cin >> l >> r;       v.push_back({l, r});       auxi[r + 1] -= 1;       auxi[l] += 1;     }     int net = 0;     for (i = 0; i <= n + 1; i++) {       net += auxi[i];       sum[i] += net;     }     int ans = 0;     for (i = 0; i < q; i++) {       for (j = 0; j <= n; j++) {         auxi[j] = sum[j];       }       int count = 0;       for (j = v[i].first; j <= v[i].second; j++) {         auxi[j]--;       }       int prefix[n + 1];       prefix[0] = 0;       for (j = 1; j <= n; j++) {         prefix[j] = prefix[j - 1] + (auxi[j] == 1);         if (auxi[j]) count++;       }       for (j = i + 1; j < q; j++) {         ans = max(ans, count - prefix[v[j].second] + prefix[v[j].first - 1]);       }     }     cout << ans <<   n ;   }   