#include <stdio.h>   
FILE *in,*o;   
int s,d,i,g,w;   
long 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",co);   
else fprintf(o,"-1");   
fclose(in);   
fclose(o);   
return 0;   
}