10分求助

#include<iostream>
using namespace std;

bool flag[10005];

int main()
{
    int l,m;
    cin >> l >> m;
    for (int i = 1;i <= m;i++)
    {
        int u,v;
        cin >> u >> v;
        for (int j = u;j <= v;j++)
        {
            if (flag[j] == false)
            {
                flag[j] = true;
            }
        }
    }
    int cnt = 0;
    for (int i = 1;i <= l;i++)
    {
        if (!flag[i])
        {
            cnt++;
        }
    }
    cout << cnt << endl;
    return 0;
}