#include<fstream>
using namespace std;
ifstream in("energii.in");
ofstream out("energii.out");
int inf,g,w,i,j,e,c,a[5002];
int main(){
	inf=2000000000;
    in>>g>>w;
    for(i=1;i<=w;i++)
		a[i]=inf;
    for(i=1;i<=g;i++){
		in>>e>>c;
		for(j=0;j<=w-e;j++)
			if(a[j]+c<a[j+e])
				a[j+e]=a[j]+c;}
	if(a[w]!=inf)
		out<<a[w];
	else out<<-1;
    return 0;}