#include <fstream>
#include <algorithm>
using namespace std;
ifstream in ("energii.in");
ofstream out ("energii.out");
struct info
{
    int energie;
    int valoare;
    double raport;
};
bool sortare (info a, info b)
{
    return a.raport>b.raport;
}
info v[1001];
int g,n;
int main()
{
    in>>n>>g;
    for (int i=1;i<=n;++i)
    {
        in>>v[i].energie>>v[i].valoare;
        v[i].raport=1.0*v[i].energie/v[i].valoare;
    }
    sort(v+1,v+n+1,sortare);
    int e=0,cnt=1,s=0;
    while (e<g && cnt<=n)
    {
        s+=v[cnt].valoare;
        e+=v[cnt++].energie;
    }
    if (e<g)
        out<<-1;
    else
        out<<s;
    return 0;
}