#include <fstream>
#include <climits>
using namespace std;

ifstream f("energii.in");
ofstream g("energii.out");

int v[5009],gr,w,e,c,i,j;
int main()
{
    f >> gr >> w ;

    for ( i = 1 ; i <= w ; i ++ )
         v[i]=INT_MAX;
    for ( i = 1 ; i <= gr ; i ++ )
    {
        f >> e >> c;
         for ( j = w ; j >= 1 ; j -- )
         {
             if ( e >= j)
                v[j] = min(v[j],c);
                 else
                 if(v[j-e] != INT_MAX)
                  v[j] = min(v[j],v[j-e]+c);
         }
    }

 if ( v[w] == INT_MAX )
     g << '-1';
  else
    g << v[w];
    return 0;
}