#include<iostream>
#include<fstream>
#include<algorithm>
using namespace std;
int a[1002],b[1002];
int main ()
{
	int g,w;
	long long min=2000000000;
	ifstream fin ("energii.in" );
	ofstream fout("energii.out");
	fin>>g>>w;
	for (int i=1;i<=g;i++) fin>>a[i]>>b[i];
	a[g+1]=-1;
	for (int i=1;i<=g-1;i++)
		for (int j=i+1;j<=g;j++)
			if (a[i]>a[j])
			{
				int aux;
				aux=a[i];
				a[i]=a[j];
				a[j]=aux;
				aux=b[i];
				b[i]=b[j];
				b[j]=aux;
			}
	int s;
	for (int i=1;i<=g;i++)
	{
		int j=i;s=0;
		int cost=0;
		while (s<w && a[j]!=0)
		{
			s+=a[j];
			cost+=b[j];
			j++;
		}
		if(cost<min) min=cost;
		if(a[j]==0) {
			min=-1;
			break;
		}
		
	}
	fout<<min;
	return 0;
}