#include<stdio.h>

int main(void) {int sz[10001];
	for (int i = 0;i < 10001;i++)
		sz[i] = 0;
	int l, u, v,m,num=0;
	scanf("%d%d", &l, &m);
	
	for (int i = 0;i < m;i++)
	{
		scanf("%d%d",&u,&v);
		for (int j = u-1;j < v;j++)
			sz[j] = 1;
	}
	for (int i = 0;i < l;i++)
		if (sz[i] == 1)
			num += 1;
	printf("%d", l-num+1);
	return 0;
}