#include <iostream>
#include <fstream>
#include <stdio.h>
using namespace std;
long int g,w,a[100],b[100];
void citeste()
{
    int i;
    ifstream f ("energii.in");
    f>>g;
    f>>w;
    for(i=0;i<g;i++)
    {
        f>>a[i];
        f>>b[i];
    }
    f.close();
}
void sorteaza()
{
    int inv=1,aux,i;
    do{
        inv=0;
        for(i=0;i<g-1;i++)
            if((a[i]/b[i]<a[i+1]/b[i+1])&&(b[i]>=b[i+1]))
            {
                inv=1;
                aux=a[i];
                a[i]=a[i+1];
                a[i+1]=aux;
                aux=b[i];
                b[i]=b[i+1];
                b[i+1]=aux;
            }

        }while(inv);
}
int calculeaza()
{
    int i,s=0,z=0;
    for(i=0;i<g;i++)
        {
        s=s+a[i];
        z=b[i]+z;
        if(s>=w)
            return z;
        }
return -1;

}
int main()
{
citeste();
sorteaza();
ofstream h ("energii.out");
h<<calculeaza();
h.close();

    return 0;
}