#include<iostream>
#include<fstream>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int N,W,i,j,t;
int e[1002],c[1002];
int a[1002][5002];

int main()
{
    f>>N>>W;
    for (i=1;i<=N;i++)
        {f>>e[i]>>c[i];t+=e[i];}
    if (t<W)
        g<<-1;
    else
    {
        for (i=0;i<N;i++)
        {
            for (j=1;j<=W;j++)
            {
                a[i][j]=350000;
            }
        }
        for (i=1;i<=N;i++)
        {
            for (j=1;j<=W;j++)
            {
                if (e[i]>=j)
                    a[i][j]=min(a[i-1][j],c[i]);
                else
                    a[i][j]=min(a[i-1][j],a[i-1][j-e[i]]+c[i]);
            }
        }
        /*for (i=1;i<=N;i++)
        {
            for (j=1;j<=W;j++)
            {
                cout<<a[i][j]<<' ';
            }
            cout<<'\n';
        }*/
        g<<a[N][W]<<'\n';
    }
    f.close();g.close();
    return 0;
}