#include <stdio.h>
FILE *in,*o;
int s,d,i,g,w,co;
float a,f[1003],e[1003],c[1003];
int main()
{
in=fopen("energii.in","r");
o=fopen("energii.out","w");
fscanf(in,"%d",&g);
fscanf(in,"%d",&w);
for (i=1;i<=g;i++)
 {
 fscanf(in,"%f%f",&e[i],&c[i]);
 f[i]=c[i]/e[i];
 }
d=0;
while (d==0)
 {
 d=1;
 for (i=1;i<g;i++)
  if (f[i]>f[i+1])
   {
   a=f[i];
   f[i]=f[i+1];
   f[i+1]=a;
   a=e[i];
   e[i]=e[i+1];
   e[i+1]=a;
   a=c[i];
   c[i]=c[i+1];
   c[i+1]=a;
   d=0;
   }

 }
s=0;
for (i=1;i<=g && s<w;i++)
 {
 s=s+e[i];
 co=co+c[i];
 }
if (s>=w)
 fprintf(o,"%d",int(co));
else fprintf(o,"-1");
fclose(in);
fclose(o);
return 0;
}