#include <cstdio>
#define INF "energii.in"
#define OUF "energii.out"
#define NMAX 10002

int main()
{
	FILE *in,*out;
	int mem[NMAX]={0},v[NMAX]={0},e,c,i,j,n,w,min;
	in=fopen(INF,"r");
	out=fopen(OUF,"w");
	fscanf(in,"%d %d",&n,&w);
	for(i=1;i<=n;++i)
	{
		for(j=1;j<NMAX;++j) mem[j]=v[j];
		
		fscanf(in,"%d %d",&e,&c);
		if(mem[e]>c||mem[e]==0) v[e]=c;
		for(j=e+1;j<NMAX;++j)
			if(mem[j-e])
			{
			       	if(mem[j]&&mem[j]>mem[j-e]+c) v[j]=mem[j-e]+c;
				else if(mem[j]==0) v[j]=mem[j-e]+c;
			}
	}
	min=1<<24;e=0;
	for(i=w;i<NMAX;++i)
		if(v[i]&&v[i]<min){ min=v[i];e=1;}
	if(e) fprintf(out,"%d\n",min);
	else fprintf(out,"-1\n");
	fclose(in);fclose(out);
	return 0;
}