// energii.cpp : Defines the entry point for the console application.
//

#include <cstdio>
#include <string.h>
int g,w;
int energie[1001],cost[1001];
#define INF 10000008
# define VAR 20001
int e[VAR],t=0;
bool uz[VAR];
void citire()
{
	scanf("%d",&g);
	scanf("%d",&w);
	for(int i=1;i<=g;i++)
	{
		scanf("%d %d",&energie[i],&cost[i]);
		t=t+energie[i];
	}
}
void marcare()
{
	for(int i=1;i<=VAR;i++)
		e[i]=INF;
}
void rezolvare()
{
	int en,i;
	for(en=1;en<=w;en++)
	{
		for(i=0;i+en<=VAR;i++)
			if(e[i]!=INF)
				if(!uz[i] && e[i+en]>e[i]+cost[en])
				{
					e[i+energie[en]]=e[i]+cost[en];
					uz[i+energie[en]]=1;
				}
		memset(uz,0,VAR);
	}
}
int scrie()
{
	int i,max=INF;
	for(i=w;i<=5500;i++)
		if(e[i]<=max)
			max=e[i];
	if(max==INF)
		return -1;
	else
		return max;
}
int main()
{
	freopen("energii.in","r",stdin);
	freopen("energii.out","w",stdout);
	citire();
	marcare();
	if(t<w)
	{
		printf("-1");
		return 0;
	}
	rezolvare();
	printf("%d",scrie());
	return 0;
}