#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream f("energii.in");
    ofstream g("energii.out");
    float cmin,e,c,auxe,auxc,aux,x[1000],y[1000],z[1000];
    int i,G,test,w;
    test=0;
    cmin=0;
    f>>G;
    f>>w;
    for(i=1;i<=G;i++)
    {
        f>>e>>c;
        z[i]=e/c;
        x[i]=e;
        y[i]=c;
    }
    while(!test)
    {
        test=1;
        for(i=0;i<=G-2;i++)
            if(z[i]>z[i+1])
            {
                aux=z[i];
                auxe=x[i];
                auxc=y[i];
                z[i]=z[i+1];
                x[i]=x[i+1];
                y[i]=y[i+1];
                z[i+1]=aux;
                x[i+1]=auxe;
                y[i+1]=auxc;
                test=0;
            }
    }
    while((w>0) && (G>0))
    {
        w=w-x[G];
        cmin=cmin+y[G];
        G=G-1;
    }
    if(w>0)
        cmin=-1;
    g<<cmin;
    f.close();
    g.close();
    return 0;
}