只过了50， 为什么？

#include <bits/stdc++.h>
#define int long long

using namespace std;

void solved()
{
    int n, m;
    cin >> n >> m;

    vector<pair<int, int>> a(m + 1);
    for (int i = 1; i <= m; i ++ )
    {
        int x, y;
        cin >> x >> y;
        a[i] = {x, y};
    }   

    int ans = 0;
    vector<pair<int, int>> l;
    for (int i = m; i >= 1; i -- )
    {
        ans ++;
        if (i == m) 
        {
            ;
        }
        else
        {
            int h, k;
            h = l[0].first, k = l[0].second;
            for (auto [x, y] : l)
            {

                if (x > k)
                {
                    h = x; 
                    k = y;
                }
                else k = max(k, y);

                if (h <= a[i].first && k >= a[i].second)
                {
                    ans --;
                    break;
                }
            }

        }
        l.push_back(a[i]);
        sort(l.begin(), l.end());
    }

    cout << ans;
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int T = 1;
    // cin >> T;
    while (T -- )
    {
        solved();
    }

    return 0;
}