//#include <iostream>
#include <fstream>

using namespace std;

ifstream cin("energii.in");
ofstream cout("energii.out");

const int NMAX=10005;
const int oo=1<<29;
int g,w,c[NMAX],e[NMAX],a[NMAX][NMAX];
int main(){
 cin >>g>>w;
 for(int i=1;i<=g;i++){
 	cin >>e[i]>>c[i];
 }	
 for(int i=1;i<=g;i++){
 	for(int j=1;j<=w;j++){
 		a[i][j]=oo;
	 }
 }
  for(int i=1;i<=g;i++){
 	for(int j=1;j<=w;j++){
 	
 		if(e[i]<=j){
 			a[i][j]=min(a[i][j],c[i]+a[i-1][j-e[i]]);
		 }else a[i][j]=min(a[i][j],c[i]);
		 //cout <<a[i][j]<<" ";
	 }
	// cout <<"\n";
 }
if(a[g][w] != oo)cout <<a[g][w];
else cout <<-1;

return 0;
}