#include <iostream>
#include <fstream>
using namespace std;
ifstream f("energii.in");
ofstream u("energii.out");
unsigned int g,w,i,e[100000],c[100000],se,S
,sc;
double r[100000],mx;
int main()
{
    f>>g>>w;
    for (i=1;i<=g;i++) {f>>e[i]>>c[i]; S=S+e[i]; r[i]=(double)e[i]/c[i];}
    if (S>=w)
    {
    while (se<w)
    {
    for (i=1;i<=g;i++)
        if (mx<r[i]) mx=(double)r[i];
    for (i=1;i<=g;i++)
        if (mx==r[i]) {se=se+e[i]; sc=sc+c[i]; mx=0; r[i]=0; break;}

    }u<<sc;
    }
    else u<<"-1";

    return 0;
}