是不是有什么细节被我漏掉了

#include<iostream>
using namespace std;
int a[10000] = { 0 }, b[200];
int main()
{
	int l;
	cin >> l;
	for (int i = 0; i < l+1; i++) { a[i] = 1; }
	int m;
	cin >> m;
	for (int i = 0; i < 2 * m; i++) { cin >> b[i]; }
	int n = 0;
	for (int i = 0; i < m; i++)
	{
		for (int p = b[n] - 1; p < b[n + 1]; p++) { a[p] = 0; }
		n += 2;
	}
	int sum = 0;
	for (int i = 0; i < l+1; i++)
	{
		if (a[i] == 1) { sum++; }
	}
	cout << sum << endl;
	return 0;

}