#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin ("energii.in");
ofstream fout ("energii.out");

struct generator{
    int e, c;
}v[5000];

int comparare (generator a, generator b){
    return (a.e * b.c >= b.e * a.c);
}

int main()
{
    int g, w, rez=0;
    fin>>g>>w;
    for(int i=0; i<g; i++){
        fin>>v[i].e>>v[i].c;
    }

    sort(v, v+g, comparare);

    for(int i=0; i<g && w>0; i++){
        if(v[i].e <= w){
            w -= v[i].e;
            rez += v[i].c;
        }
    }

    fout<<rez;
}