#include <bits/stdc++.h>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int n,m,i,s,p;
struct elem{
double energie,cost,raport;
}v[10001];
int compara(elem a, elem b)
{
    if(a.raport<b.raport)
        return 0;
    return 1;
}
int main()
{
    f>>n;
    f>>m;
    for(i=1;i<=n;i++)
    {
        f>>v[i].energie>>v[i].cost;
        v[i].raport=v[i].energie/v[i].cost;
    }
    sort(v+1,v+n+1,compara);
    for(i=1;i<=n;i++)
    {
        s=s+v[i].energie;
        p=p+v[i].cost;
        if(s>=m)
        {
            g<<p;
            return 0;
        }
    }
    g<<-9;
}