怎么改都不对，结果加一后七个对，不加前三个对，实在没辙了

#include <bits/stdc++.h>
using namespace std;
int a[10000000],b[10000000],l[100000000];
int main() {
	int n,m;
	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		l[i] = 0;
	}
	for (int i = 0; i < m; i++) {
		cin >> a[i] >> b[i];
	}
	for (int i = 0; i < m; i++) {
		for (int j = a[i]; j <= b[i]; j++) {
			l[j] = 1;
		}
	}
	int s = 0;
	for (int i = 0; i < n; i++) {
		if (l[i] == 0) {
			s++;
		}
	}
	cout << s << endl;
	return 0;
}