#include <fstream>

using namespace std;

ifstream f("energii.in");
ofstream g("energii.out");
int costmin[1005][5001];
long long s,nr;
int main()
{
    int e[1005],w,cost[1005],y;
    f>>nr>>w;
    for (int i=1; i<=nr; ++i)
    {
        f>>e[i]>>cost[i];
        s+=e[i];
    }
    for (int i=1; i<=w; ++i) costmin[0][i]=2000000000;
    for (int i=1; i<=nr; ++i) costmin[i][0]=2000000000;
    for (int i=1; i<=nr; ++i)
     for (y=1; y<=w; ++y)
     {
         if (e[i]>=y)
         {
             costmin[i][y]=min(costmin[i-1][y],cost[i]);
         }
         else
         {
             costmin[i][y]=min(costmin[i-1][y],costmin[i-1][y-e[i]]+cost[i]);
         }
     }
    if (s<w) g<<-1<<'\n';
     else g<<costmin[nr][w]<<'\n';

    f.close();
    g.close();
    return 0;
}