#include <stdio.h>
#define Wmax 5000
#define INF 2000000000
#define Gmax 1000

int G, W, cost[Wmax+1], req[Gmax+1], gain[Gmax+1];

void read()
      {
	   int i;		
	   
	   freopen("energii.in","r",stdin);
	   
	   scanf("%d\n%d\n",&G,&W);
	   for(i=1;i<=W;i++)
				cost[i]=INF;
	   for(i=1;i<=G;i++)
		       scanf("%d %d",&gain[i],&req[i]), cost[gain[i]]=req[i];
	   
	   fclose(stdin);
	  }
void solve()
	{
	 int i, j;	 
		
	 for(i=1;i<=G;i++)
		 for(j=1;j<=W;j++)
			    if(gain[i]<j && cost[ j-gain[i] ]+req[i]<cost[j])
					  cost[j]=cost[ j-gain[i] ]+req[i];
	}
void write()
	{
	 freopen("energii.out","w",stdout);
	 if(cost[W]==INF) 
		     printf("-1\n");
	 else
	         printf("%d\n",cost[W]);
	 fclose(stdin);
	}
int main()
	{
	 read();
	 solve();
	 write();
	 return 0;
	}