#include <stdio.h>
#include <iostream>
#include <fstream>

using namespace std;

int big[5005];
int c[1001],w[1001];

int main(){

    int n,m,i,j,k;
    
    ifstream  in("energii.in" );
    ofstream out("energii.out");   
    
    in >> n >> m;
        
    for (i=0;i<n;i++)
      in >> w[i] >> c[i];
      
    for (i=0;i<n;i++)  
      for (j=0;j<m;j++)
        if (!big[j]){
        int rel = j + w[i];
        if (rel > m) rel = m;
        int val = big[j] + c[i];
        if (!big[rel] || (big[rel] > val )) 
          big[rel] = val;
        }   
    
    if (big[m] == 0) out << -1;
      else out << big[m];
                      
    in.close();            
    out.close();    
    
    return 0;
}