2012百度之星J題

#include"stdio.h"
int main()
{
 int i,j,mid,low,high,min=0x7fffffff,m,n,u,d,tmp;
 scanf("%d%d",&n,&m);
 while(m--)
 {
  scanf("%d%d",&u,&d);
  low=1,high=n;
  while(high-low>2)
  {
      mid=(high+low)/2;
            tmp=u*mid-d*(n-mid);
   if(tmp>0)
    high=mid;
   else
    low=mid;
  
  }
  for(i=low;i<=high;i++)
  {
   tmp=u*i-d*(n-i);
   if(tmp>0)break;
  }
  if(min>tmp)min=tmp;
 }
 printf("%d\n",min);
 return 0;
}