#include<stdio.h>
#include<algorithm>
using namespace std;
int En,E[100000],C[100000],ok,s,i,W,G;
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]);
	}
	if(s<W)
		printf("-1");
	else
	{
	do
	{
		ok=1;
		for(i=1;i<G;i++)
			if(C[i]>C[i+1]&&E[i]<E[i+1])
				{swap(C[i],C[i+1]);
				swap(E[i],E[i+1]);ok=0;
				}
	}while(ok==0);
	
	while(En<=W&&i<=G)
	{
		En+=E[i];
		i++;
		
	}
	if(En<W&&i<G)
	{En+=E[++i];
	}
	printf("%d",En);
	}
	
	
	return 0;
}