#include <bits/stdc++.h>
using namespace std;
bool a[10005];
int main()
{
	int n;
	cin >> n;
	int m;
	cin >> m;
	for (int i = 0 ; i < n ; i++)
	{
		a[i] = true;
	}
	int cnt = 0;
	for (int i = 1 ; i <= m ; i++)
	{
		int c, b;
		cin >> c >> b;
		for (int i = c - 1; i < b ;i++)
		{
			if(a[i] == true)
			{
				cnt++;
				a[i] = false;
			}
		}
	}
	cout << n - cnt + 1  << endl;
}