while(l<r)
    {
      int mid=(l+r)>>1;
      if(a[mid]>=m)r=mid;
      else l=mid+1;
    }

    while(l<=r)
    {
      int mid=(l+r)>>1;
      if(a[mid]>=m)r=mid-1;
      else l=mid+1;
    }

    while(l<r)
    {
      int mid=(l+r)>>1;
      if(a[mid]>=m)r=mid-1;
      else l=mid;
    }
}