#include <stdio.h>
int main()
{
	int arr[100000] = { 0 };
	int l = 0, n = 0;
	scanf("%d %d", &l, &n);
	for (int i = 0; i < l; i++)
	{
		arr[i] = i;
	}
	for (int j = 0; j < n; j++)
	{
		int a, s;
		scanf("%d %d", &a, &s);
		for (a; a <= s; a++)
		{
			if (arr[a] != 0)
			{
				arr[a] = 0;
				l--;
			}
		}
		a = 0;
		s = 0;
	}
	printf("%d", l+1);
	return 0;
}