#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream in("energii.in");
ofstream out("energii.out");
struct generator{
    int ener, cost;
    float rand;
};
bool cmp(generator a, generator b)
{
    return a.rand>b.rand;
}
int main()
{
    int n, w;
    in>>n>>w;
    generator gen[n];
    for(int i=0;i<n;++i)
    {
        in>>gen[i].ener>>gen[i].cost;
        gen[i].rand=(float)gen[i].ener/gen[i].cost;
    }
    sort(gen, gen+n, cmp);
    int cnt=0, tc=0;
    while(w>0&&cnt<n)
    {
        tc+=gen[cnt].cost;
        w-=gen[cnt].ener;
        cnt++;
    }
    if(w<=0)
        out<<tc<<"\n";
    else
        out<<"-1\n";
    return 0;
}