#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int n,e,i,cost;
struct generator
{
    float p,c,r;
}v[1002];
bool comp (generator a,generator b)
{
    if(a.r<b.r) return false;
    return true;
}
int main()
{
    f >> n >> e;
    for(i=1; i<=n; i++) {
        f >> v[i].p >> v[i].c;
        v[i].r=(float)v[i].p/v[i].c;
    }
    sort(v+1,v+n+1,comp);
    i=1;
    while(i<=n and e>0) {
        e-=v[i].p;
        cost+=v[i].c;
        i++;
    }
    g << cost;
    return 0;
}