#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
const int inf=6010005;
int d[5005];
int main()
{
    int i, wn, j, e, c, n;
    fin>>n>>wn;
    for(i=1;i<=wn;i++)
    {
        d[i]=inf;
    }
    for(i=1;i<=n;i++)
    {
        fin>>e>>c;
        for(j=wn;j>=0;j--)
           {
               if(d[j]!=inf and j+e<=wn)
               {
                   d[j+e]=min(d[j+e], d[j]+c);
               }
           }
    }
    if(d[wn]==inf)
    {
        fout<<-1<<"\n";
    }
    else
       fout<<d[wn]<<"\n";
    return 0;
}