#include<fstream>
using namespace std;
#define nmax 1002
#define inf 0x3f3f3f3f
ifstream f("energii.in");
ofstream g("energii.out");
int w[nmax],c[nmax],n,m,a[nmax][5002];
int mini(int b, int d)
{
	if(b<d) return b;
	else return d;
}
int main()
{	f>>n>>m;
	for(int i=1;i<=n;i++)
		f>>w[i]>>c[i];
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++)
			a[i][j]=inf;
	int s=0,s2=0;
	for(int i=1;i<=n;i++)
	{
		s=s+w[i];
		s2=s2+c[i];
		for(int j=1;j<=m;j++)
		{
			if(i==1)
			{
				if(j<=w[i])
					a[i][j]=c[i];
				continue;
			}
			if(j<=w[i])
				a[i][j]=mini(a[i-1][j],c[i]);
			else
				a[i][j]=mini(a[i-1][j],a[i-1][j-w[i]]+c[i]);
		}
	}
	if(a[n][m]==inf)
		g<<"-1";
		else
			g<<a[n][m];
	f.close();g.close();
		return 0;}