#include<fstream>
#define inf 2000000000
using namespace std;
int n,s,sol[5002],C[1002],G[1002],i,j;
char uz[5003][1003];
int main()
{
	ifstream f("energii.in");ofstream g("energii.out");
	f>>n>>s;
	for(i=1;i<=n;i++)
		f>>G[i]>>C[i];
	for(i=1;i<=s;i++)
	{ sol[i]=inf;
		for(j=1;j<=n;j++)
		  if(sol[i-G[j]]+C[j]<sol[i] && !uz[i-G[j]][j] && G[j]<=i)
		  {
			sol[i]=sol[i-G[j]]+C[j];
			uz[i][j]='1';
		  }
	}
	if(sol[s]==inf)g<<"-1"; else 
	g<<sol[s]<<'\n';
	f.close();g.close();
return 0;}