#include<iostream>
#include<malloc.h>
using namespace std;
int main()
{
	
	bool* p;
	p=(bool*)malloc(10001 * sizeof(int));
	if (p == NULL) { cout << "default"; return 0; }
	memset(p, 1, 10001);
	int n, num_1;
	
	cin >> n >> num_1;
	while (num_1--)
	{
		int a, b;
		cin >> a >> b;
		for (int i = a; i <= b; i++)
		{
			p[i] = 0;
		}

	}
	int ans = 0;
	for (int i = 0; i <= n; i++)
	{
		if(p[i])
		ans++;
	}
	free(p);
	cout << ans;
return 0;
}