#include<iostream>
#include<bits/stdc++.h>
using namespace std;


int main()
{
	int l, m,n=0;
	cin >> l >> m;
	int u, v;
	bool a[10001];
	memset(a, 0, sizeof(a));

	for (int i = 0; i < m; i++)
	{
		cin >> u >> v;
		for (int i = u; i <= v; i++)
			a[i] = 1;
	}
	for (int i = 0; i < l; i++)
	{
		if (a[i] == 1) n++;
	}
	cout << l+1-n << endl;
	return 0;
}