#include<stdio.h>
int main()
{
	int l, m;//l表示马路长度，m表示有多个区域；
	int i, j;
	int count, vis[10001];
	int head, tail;
	count = 0;
	scanf("%d%d", &l, &m);
	for (i = 0; i <= l; i++)
	{
		vis[i] = 0;//标记马路上的树
	}
	for (i = 1; i <= m; i++)
	{
		scanf("%d%d", &head, &tail);
		for (j = head; j <= tail; j++)
		{
			if (vis[j] = 0)
				vis[j] = 1;//树被砍
		}
	}
	for (i = 0; i <= l; i++)
		if (vis[i] = 0)
			count++;
   return 0;
}