#include <stdio.h>


int i,j,k,g,w,x,y,a[2000],b[2000],min,st[2000],p,s;


//void init() {st[k]=-1;}

int Am_Succ()
  { if (st[k]<1)
	  {if ((st[k]==0) && (b[k]>min)) return 0;
	   st[k]++;
	   s+=a[k]*st[k];
	   p+=b[k]*st[k];
	   return 1;
	   }
	else return 0;
  }

void back()
  {int as;
   k=1;st[k]=-1;
   while (k>0)
      {do {as=Am_Succ();
	   }
       while (as && (p>min));
       if (as) if ((s>=w) || (k==x)) if ((s>=w) && (p<min)) min=p;
						       else {}
			      else {k++;st[k]=-1;}
	else {s-=a[k]*st[k];
	      p-=b[k]*st[k];
	      k--;
	      }
      }
  }


int main()
{
FILE *fin,*fout;

fin=fopen("energii.in","r");
fscanf(fin,"%d",&g);
fscanf(fin,"%d",&w);

s=0;
for (i=1;i<=g;i++)
  {fscanf(fin,"%d",&x);
   fscanf(fin,"%d",&y);
   j=1;
   s+=x;
   while ((j<=i-1) && (a[j]<x)) j++;
   for (k=i-1;k>=j;k--)
     {a[k+1]=a[k];
      b[k+1]=b[k];
      }
   a[j]=x;
   b[j]=y;
   }
fclose(fin);

i=1;
while ((i<=g) && (a[i]<w)) i++;
x=i-1;
if (x+1<=g) min=b[x+1];
       else min=32000;
for (i=x+1;i<=g;i++)
  if (min>b[i]) min=b[i];

if (s>=w){ p=s=0; back();}
    //else if (s==w) min=s;
	      else min=-1;

fout=fopen("energii.out","w");
fprintf(fout,"%d",min);
fclose(fout);
return 0;
}