#include <iostream>
using namespace std;

int main() {
	int l, m, u, v, a[10005] = {0}, p = 0;
	cin >> l >> m;
	for (int i = 0; i < m; i++) {
		cin >> u >> v;
		for (int j = u; j <= v; j++) {
			a[j] = 1;
		}
	}
	for (int i = 0; i <= l; i++) {
		if (a[i] == 0)
			p++;
	}
	cout << p << endl;
	return 0;
}

请问这个数组开的大小为什么必须比10000大一点，不能是10000呢？qwq