#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define min(x,y) (x>y?y:x)
FILE *f=fopen("energii.in","r"), *g=fopen("energii.out","w");
struct nod {int cant,cost;} a[1024];
int n,w,i,j,ok;
long long dp[5005];
bool x[5005];
int comp(nod *a, nod *b)
{
	if(a->cant > b->cant) return 1;
	else if(a->cant == b->cant) if(a->cost > b->cost) return 1;
	return -1;
}
int main()
{
	fscanf(f,"%d %d",&n,&w);
	for(i=1;i<=n;i++) fscanf(f,"%d %d",&a[i].cant,&a[i].cost);
	fclose(f);
	
	//qsort(a+1,n,sizeof(nod),(int (*)(const void *, const void *))comp);
	long long sum=0; 
	for(i=1;i<=n;i++) sum+=a[i].cant;
	if(sum<(long long)w)  fprintf(g,"-1\n");
		else{
	memset(dp,0x3f3f3f3f,sizeof(dp));
	x[0]=1;
    dp[0]=0;
    x[a[1].cant]=1;
    dp[a[1].cant]=a[1].cost;
	
	for(i=2;i<=n;i++)
		for(j=w;j>=0;j--)
			if(x[j])
			{
				if(j+a[i].cant>=w)
				{
                    //fprintf(g,"%d %d %d\n", j+a[i].cant, j, dp[j]+a[i].cost);
					x[w]=1;
					dp[w]=min(dp[j]+a[i].cost, dp[w]);
				}
				else 
					{
						x[j+a[i].cant]=1;
						dp[j+a[i].cant]=min(dp[j]+a[i].cost, dp[j+a[i].cant]);
					}
			}
		
		fprintf(g,"%lld\n",dp[w]);
		}
	
	fclose(g);
	return 0;
}