#include<stdio.h>
int main()
{
	int i, j, l, m, z = 0;
	scanf("%d%d", &l, &m);
	int S[110], SS[110], b[11000];
	for (i = 0; i < m; i++)
		scanf("%d%d", &S[i], &SS[i]);
	for (i = 0; i < l ; i++)
		b[i] = 0;
	for (i = 0; i < m; i++) {
		for (j = S[i]; j <= SS[i]; j++)
			b[j] = 1;
	}
	for (i = 0; i < l + 1; i++)
		if (b[i] == 0)
			z++;
	printf("%d", z + 1);
	return 0;
}