//
//  main.cpp
//  Energii
//
//  Created by Albastroiu Radu on 9/4/16.
//  Copyright © 2016 Albastroiu Radu. All rights reserved.
//

#include <iostream>
#include <fstream>
#include <algorithm>
#include <unordered_map>
#include <vector>
#define MULTFOARTEMULT (1<<28)-1
using namespace std;

ifstream fin("energii.in");
ofstream fout("energii.out");

int i,j,nr_of_gen, min_power, power, cost, cost_total[11001], Min_cost;

int main()
{
    
    fin >> nr_of_gen >> min_power;
    
    for(i=1;i<=10001;i++)
        cost_total[i]=MULTFOARTEMULT;
    
    Min_cost = MULTFOARTEMULT;
    
    for(i=1;i<=nr_of_gen;i++)
    {
        fin >> power >> cost;
        
        for(j=min_power-1;j>=0;j--)
        {
            cost_total[j + power] = min(cost_total[j + power], cost_total[j] + cost);
            
            if(j+power >= min_power)
            {
                Min_cost = min(Min_cost, cost_total[j+power]);
            }
        }
        
        cost_total[power]=min(cost_total[power],cost);
        if(power>min_power)
        {
            Min_cost = min(Min_cost, cost);
        }
        
    }
    
    if(Min_cost!=MULTFOARTEMULT)
        fout<<Min_cost;
    else
        fout<<-1;
    
    return 0;
}