#include<fstream>
using namespace std;
int i,j,n,g,s;
struct en
{
    int e,c;
};
int main()
{en v[100],aux;
    ifstream fer("energii.in");
    ofstream ger("energii.out");

    fer>>n>>g;
    for(i=1;i<=n;i++)
        fer>>v[i].e>>v[i].c;
        for(i=1;i<n;i++)
            for(j=i;j<=n;j++)
            if((float)v[i].e/v[i].c<(float)v[j].e/v[j].c)
        {
          aux=v[i];
          v[i]=v[j];
          v[j]=aux;
        }
        for(i=1;i<=n;i++)
        {if(g)
            {s=s+v[i].c;
            g=g-v[i].e;
        }}
       if(g<=0) ger<<s;
       else ger<<-1;
}