#include<stdio.h>              
#include<stdlib.h>              
#include<string.h>              
char x[35867530];              
int main()              
{              
 int n,time=0;              
 while(scanf("%s %d",x,&n)!=EOF)              
 {              
  int a,b,c=n,m=strlen(x),flag=0;  
  int set=-1;  
   for(a=0;a<c;a++,n--)              
    {              
     int max=-1;  
     for(b=set+1;b<=m-n;b++)              
      {     
       if(x[b]-48>max)        
        {              
         max=x[b]-48;              
         set=b;  
         if(max==9) break;   
        }  
      }  
      printf("%d",max);  
    }              
    printf("\n");            
 }              
 return 0;              
}  

這樣來回跑會多計算東西 也多跑很多迴圈  改如何修?