#include<stdio.h>
int main()
{
	int l, m, u[100] = { 0 }, v[100] = { 0 }, i, j, k, n;
	scanf("%d%d",&l,&m);
	for (i = 0; i < m; i++)
		scanf("%d%d",&u[i],&v[i]);
	for (i = 0; i < m; i++)
	{
		for (j = 0; j < m; j++)
		{
			if (v[i] >= u[j] && v[i] <= v[j]&&u[i]<=u[j]&&i!=j)
				v[i] = v[j], u[j] = 0, v[j] = -1;
			else if (v[i] >= v[j]&&u[i]<=u[j]&&u[i]<=v[j]&&i!=j)
				u[j] = 0, v[j] = -1;
		}
	}
	for (i = 0, k = 0; i < m; i++)
		k += v[i] - u[i] + 1;
	n = l + 1 - k;
	printf("%d", n);
	return 0;
}