#include <iostream>
#include <fstream>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int main()
{
    int ge,w,cost,k,eg[10001],cg[10001],m,l=0,i;
    f >> ge >> w;
    for (i=0;i<ge;i++)
      {
          f >> eg[i] >> cg[i];
      }
      for (i=0;i<ge;i++)
      {
           cost=cost+cg[i];
      }
    for (i=0;i<ge;i++)
    {
        m=i;
        k=0;
        l=0;
        while (k<w)
        {
            k=k+eg[i];
            i++;
            l=l+cg[i];
        }
        if ((l<cost) && (l!=0))
        {
            cost=l;
        }
        i=m;
    }
    if (k<w) g << "-1";
    else g << cost;
}