#include <stdio.h>

int v[5001],g,w,i,j,e,c;

int main()
{
	freopen("energii.in","r",stdin);
	freopen("energii.out","w",stdout);
	scanf("%d%d",&g,&w);
	for (i=1;i<g+1;i++)
	{
		scanf("%d%d",&e,&c);
		for (j=0;j<w+1;j++)
		{
			if (((v[j]!=0)||(j==0))&&((v[e+j]==0)||(v[e+j]>v[j]+c)))
				if (i+j<w) v[e+j]=v[j]+c;
				else if (v[w]>v[j]+c) v[w]=v[j]+c;
		}

	}
	if (v[w]==0) v[w]=-1;
	printf("%d",v[w]);
	return 0;
}