#include<stdio.h>
int g,w,p[1002],c[1002],a[5003][3];//,sum[5003][3],v[102];//v[0][..]energie,v[1][..]costul
void read()
{
	FILE*f=fopen("energii.in","r");
	fscanf(f,"%d%d",&g,&w);
	int i;
	for(i=0;i<g;++i)
	{
		fscanf(f,"%d%d",&p[i],&c[i]);
	}
	fclose(f);
}
int posibil(int j,int s)
{
	int aux;
	while(s)
	{
		aux=a[s][1];
		s=a[s][2];
		if(aux==j)return 0;
	}
	return 1;
}
int dinamic()
{
	int i,j,pos=1,var,ct;
	a[0][0]=0;
	for(i=1;i<=w;++i)
	{
		a[i][0]=99999999;
		for(j=0;j<g;++j)
		{
			var=i-p[j];
			if(i-p[j]<0)var=0;
			//if(!a[var][j+1]&&c[j]+a[var][0]<a[i][0])
			if(posibil(j,var)&&c[j]+a[var][0]<a[i][0])
			{
				a[i][0]=c[j]+a[var][0];pos=j;ct=var;//v[i]=a[i][0];//j+1!!!!
			}
		}
		//a[i][pos]=1;
		//sum[i][0]=pos;
		//if(ct>0)copy(ct,i);	
		a[i][1]=pos;a[i][2]=ct;
	}
	if(a[w][0]==99999999)return -1;
	return a[w][0];
}
int main()
{
	read();
	FILE*g=fopen("energii.out","w");
	fprintf(g,"%d\n",dinamic());
	fclose(g);
	return 0;
}