#include <bits/stdc++.h>
using namespace std;
ifstream in ("energii.in");
ofstream out ("energii.out");
struct info
{
    int cost;
    int energie;
};
info v[1001];
int rasp[5001];
int main ()
{
    int g,w,s=0;
    in>>g>>w;
    for (int i=1;i<=g;++i)
        {
            in>>v[i].energie>>v[i].cost;
            s+=v[i].energie;
        }
    if (s<w)
    {
        out<<'-1';
        return 0;
    }
    for (int i=1;i<=w;++i)
    {
        rasp[i]=INT_MAX;
        for (int j=1;j<=g;++j)
        {
            if (i-j>=0)
                rasp[i]=min(rasp[i],rasp[i-v[j].energie]+v[j].cost);
            else
                rasp[i]=min(rasp[i],v[i].cost);
        }
    }
    out<<rasp[w];
    return 0;
}