#include<stdio.h>
FILE *f=fopen("energii.in","r"),*q=fopen("energii.out","w");
long g,w,c,cost,s;
struct energ
{long x,y;} a[1001];
int main()
{fscanf(f,"%ld %ld",&g,&w);int i,j;
for(i=1;i<g;i++)
 for(j=i+1;j<=g;j++)
  if(a[i].x/a[i].y<a[j].x/a[j].y)
   {a[0]=a[i];
   a[i]=a[j];
   a[j]=a[0];}
for(i=1;s<=w;i++)
{s+=a[i].x;
cost+=a[i].y;
}
if(s<=w)fprintf(q,"-1");
else
fprintf(q,"%ld",cost);
return 0;
}