#include <fstream>
#import <algorithm>
#import <vector>
#import <set>
#import <deque>
using namespace std;
main()
{
    ifstream cin("energii.in");
    ofstream cout("energii.out");
    int n,k;
    cin>>n>>k;
    vector<int>a(k+1,2e9);
    a[0]=0;
    int rez=0;
    while(n--)
    {
        int c,val;
        cin>>val>>c;
        for(int i=k;i>=1;i--)
        {
            if(i<=val)
            {
                a[i]=min(a[i],c);
            }
            else
            {
                a[i]=min(a[i],a[i-val]+c);
            }
        }
    }
    if(a[k]==2e9)cout<<-1;
    else cout<<a[k];

}