#include<fstream>
using namespace std;
struct energie
{
	int e,c;
};
energie a[1001];
int n,w,i,j,k,b[1001][5001];
int main()
{
	ifstream f("energii.in");
	ofstream g("energii.out");
	f>>n>>w;
	for(i=1;i<=n;i++)
		f>>a[i].e>>a[i].c;
	b[0][0]=0;
	for(i=1;i<=w;i++)
		b[0][i]=100000;
	for(i=1;i<=n;i++)
		for(j=1;j<=w;j++)
		{
			b[i][j]=b[i-1][j];
			if(a[i].e<=j&&b[i][j]>b[i-1][j-a[i].e]+a[i].c)
				b[i][j]=b[i-1][j-a[i].e]+a[i].c;
			else
				if(b[i][j]>a[i].c&&a[i].e>j)
					b[i][j]=a[i].c;
		}
		if(b[n][w]==100000)
		g<<-1;
		else 
			g<<b[n][w];
				return 0;
}