#include<stdio.h>
#include<algorithm>
using namespace std;
	int G,W,H,e[100],c[100],i,Cost=0,Wramas,x,s;

int main()
{
	freopen("energii.in","r",stdin);
	freopen("energii.out","w",stdout);
	scanf("%d",&G);
	scanf("%d",&W);
	for(i=1;i<=G;i++)
	{
		scanf("%d",&e[i]);
		s=s+e[i];
		scanf("%d",&c[i]);
	}
	do
	{
		H=1;
		for(i=1;i<=G-1;i++)
			if(c[i]*e[i+1]<c[i+1]*e[i])
			{
				swap(c[i],c[i+1]);
				swap(e[i],e[i+1]);
				H=0;
			}
	}while(H==0);
	i=G;
	Wramas=W;
	
	if(s>=W)
	{
		while(i>=1&&Wramas!=0)
	{	if(e[i]<=Wramas)
		{
			Wramas=Wramas-e[i];
			Cost=Cost+c[i];
			i++;
		}
		else
			if(c[i]>=Cost)
			{	Cost=c[i];
				Wramas=0;
			}
	}
	printf("%d",Cost);
	}
	else
		printf("-1");
	
	
return 0;
}