#include <iostream>
#include <fstream>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
unsigned long g,w,a[10000000],b[10000000];
void citeste()
{
    unsigned i;
    ifstream f ("energii.in");
    f>>g;
    f>>w;
    for(i=0;i<g;i++)
    {
        f>>a[i];
        f>>b[i];
    }
    f.close();
}
void calculeaza2()
{
    int i,mic,j,aux;
    for(i=0;i<g;i++)
        {
        mic=i;
        for(j=i+1;j<g;j++)
            if((b[j]<b[mic])&&(a[j]>=a[mic])||labs(a[i]-b[i])<labs(a[i+1]-b[i+1]))
                mic=j;
        aux=a[i];
        a[i]=a[mic];
        a[mic]=aux;
        aux=b[i];
        b[i]=b[mic];
        b[mic]=aux;
        }
}
int calculeaza()
{
    unsigned i;
    unsigned long 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();
ofstream h ("energii.out");
calculeaza2();
h<<calculeaza();
h.close();

    return 0;
}