题解

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
	int l, m, tree[10010] = {0}, a, b, s = 0;
	cin >> l >> m;
	for (int i = 0; i < m; i++) {
		cin >> a >> b;
		for (int j = a; j <= b; j++)
			tree[j] = 1;
	}
		for (int i = 0; i <= l; i++)
			if (tree[i] == 0) s++;
		cout << s << endl;
	return 0;		
}