#include<stdio.h>
#include <iostream>
using namespace std;
int main()
{
	int l, m;
	int u[200], v[200];
	cin >> l >> m;
	for (int i = 1; i <= m; i++)
	{
		cin >> u[i] >> v[i];
	}
	int length[100001];
	for (int i = 1; i <= l; i++)
		length[i] = 1;
	for (int i = 1; i <= m; i++)
	{
		while( u[i] <= v[i])
		{
			if (length[u[i]] != 0)
			{
				length[u[i]] = 0;
				l--;
			}
			u[i]++;
		}
	}
	cout << l+1;
	return 0;
}