#include<stdio.h>
int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
        int i,a,b,j,count=0;
        int tree[10005];
        for(i=0;i<=n;i++)
        {
            tree[i]=1;
        }
        for(i=0;i<m;i++)
        {
            scanf("%d%d",&a,&b);
          for(j=a;j<=b;j++)
          {
            tree[j]=0;
          }
        }
        for(count=0,i=0;i<=n;i++)
        {
            if(tree[i])
                count++;
        }
        printf("%d\n",count);
    return 0;
}
/**************************************************************
	Problem: 2253
	User: admin
	Language: C
	Result: Accepted
	Time:53 ms
	Memory:1144 kb
****************************************************************/