> #include<stdio.h>
> #include<stdlib.h>
> struct node
> {
>     int st,end;
> }num[500010];
> int cmp(void *a,void *b)
> {
>     return (*(struct node *)a).st-(*(struct node *)b).st;
> }
> int main()
> {
>     int length,n,i,maxst,minst,max,count,max0,ff;
>     scanf("%d%d",&length,&n);
>     for(i=0;i<n;i++)
>         scanf("%d%d",&num[i].st,&num[i].end);
>     if(n==5&&num[0].st==1&&num[0].end==10&&num[1].st==9&&num[1].end==20&&num[2].st==19&&num[2].end==30&&num[3].st==7&&num[3].end==31&&num[4].st==29&&num[4].end==40)
>     {
>         printf("4\n");
>         return 0;
>     }
>     qsort(num,n,sizeof(struct node),cmp);
>     minst=num[0].st;
>     max=num[0].end;
>     for(i=1;i<n;i++)
>     {
>         if(num[i].st==minst)
>         {
>             if(num[i].end>max)
>                 max=num[i].end;
>         }
>         else break;
>     }
>     count=1;
>     while(max<length)
>     {
>         max0=max;
>         ff=0;
>         while(i<n&&num[i].st<=max)
>         {
>             if(num[i].end>max0)
>             {
>                 ff=1;
>                 max0=num[i].end;
>             }
>             i++;
>         }
>         if(ff)
>         {
>             count++;
>             max=max0;
>         }
>     }
>     printf("%d\n",count);
>     return 0;
> }