#include <iostream>
#include <cmath>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
int gt, w, s;
struct generator
{
    double energie;
    double cost;
    double eficienta;
}g[1001];
bool cmp(generator a, generator b)
{
    return a.eficienta<b.eficienta;
}
int main()
{
    fin>>gt>>w;
    for (int i=1; i<=gt; i++)
    {
        fin>>g[i].energie>>g[i].cost;
        g[i].eficienta=g[i].cost/g[i].energie;
    }
    sort(g+1, g+gt+1, cmp);
    int i=1;
    while(w-g[i].energie>=0)
    {
        s+=g[i].cost;
        w-=g[i].energie;
    }
    fout<<s;
}