#include<stdio.h>
FILE *f=fopen("energii.in","r"),*q=fopen("energii.out","w");
int i,g,cost,s,w,j;
struct asd
{int x,y,z;} a[2000];
int main()
{fscanf(f,"%d%d",&g,&w);
for(i=1;i<=g;i++)
 fscanf(f,"%d%d",&a[i].x,&a[i].y);
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].y;
cost+=a[i].x;
}
if(s<w)
fprintf(q,"-1");
else
fprintf(q,"%d",cost);
return 0;
}