#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;

ifstream f("energii.in");
ofstream g("energii.out");

struct ab
{
    int e,c; double r;
} a[1001];

int n,m,sol;

void citire()
{
    f>>n>>m;
    for(int i=1;i<=n;i++)
    {
        f>>a[i].e>>a[i].c;
        a[i].r=double (a[i].e)/a[i].c;

    }

}
bool comp(ab x,ab y)
{
    return (x.r>y.r);
}

void solve()
{

    sort(a+1,a+n+1,comp);
    int s=0;
    for(int i=1;s<m;i++)
    {
        s+=a[i].e;
        sol+=a[i].c;
    }
}

int main()
{
    citire();
    solve();
    /*for(int i=1;i<=n;i++)
    {
      cout<<a[i].e<<" "<<a[i].c<<" "<<(double) a[i].r<<"\n";
    }
    */
    g<<sol;

    return 0;
}