#include<fstream.h>
long sum=0;
float c[1001],aux;
int a[1001],b[1001];
int main()
{
int i,j,p,w,nr=0,ok=1;
ifstream f("energii.in");
ofstream g("energii.out");
f>>p>>w;
for(i=1;i<=p;i++)
	{
	f>>a[i]>>b[i];
	c[i]=(float)b[i]/a[i];
	}
for(i=1;i<=p;i++)
	for(j=i+1;j<=p;j++)
		{
		if(c[i]>c[j])
			{
			aux=c[i];
			c[i]=c[j];
			c[j]=aux;
			aux=a[i];
			a[i]=a[j];
			a[j]=aux;
			aux=b[i];
			b[i]=b[j];
			b[j]=aux;
			}
		}
for(i=1;i<=p&&ok==1;i++)
	{
	sum=sum+b[i];
	nr=nr+a[i];
	if(nr>=w)
		ok=0;

	}
if(sum>=w)
g<<sum;
else
g<<-1;



f.close();
g.close();
return 0;
}