#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
int n,gmax,pt,i;
    struct ruc
    {
        int p,g;
        int o;
    }v[5001];
int compar(ruc a,ruc b){
return a.p*b.g>b.p*a.g;}
int main()
{
    ifstream f("rucsac.in");
    ofstream h("rucsac.out");

    f>>n>>gmax;
    for(i=1;i<=n;i++) f>>v[i].g>>v[i].p;
    sort(v+1,v+n+1,compar);
    i=1;
    while(gmax>0&&i<=n)
    {

        if(v[i].g<=gmax) {pt+=v[i].p;gmax-=v[i].g;}
        i++;
    }
    h<<pt;
    f.close();
    h.close();
    return 0;
}