#include <iostream>
#include <fstream>

using namespace std;

const int GMAX2=5000,INF=2000000000;
int d[GMAX2+5];

struct centrala
{
    int e,c;
};

centrala v[1005];

ifstream fin("energii.in");
ofstream fout("energii.out");

int main()
{
    int n,i,j,last,minim,GMAX;
    fin>>n>>GMAX;
    for(i=1; i<=n; i++)
        fin>>v[i].e>>v[i].c;
    for(i=1; i<=GMAX; i++)
        d[i]=INF;
    d[0]=0;
    last=0;
    minim=INF;
    for(i=1; i<=n; i++)
    {
        for(j=last; j>=0; j--)
        {
            if(d[j]!=INF && j+v[i].e<=GMAX && d[j+v[i].e]>d[j]+v[i].c)
                d[j+v[i].e]=d[j]+v[i].c;
            if(j+v[i].e>=GMAX && d[j]!=INF && minim>d[j]+v[i].c)
                minim=d[j]+v[i].c;
        }
        last=min(last+v[i].c,GMAX);
    }
    if(minim==INF)
        fout<<-1;
    else fout<<minim;
}