#include <iostream>
#include <fstream>
using namespace std;
ifstream f("energii.in");
ofstream h("energii.out");
int n,e,cost;
struct generatoare
{
    int e,c;
}g[1001];
void citire()
{
    f>>n>>e;
    for(int i=1;i<=n;i++)
    f>>g[i].e>>g[i].c;
}
void solve()
{
    int var=0;
    for (int i=1;i<n;i++)
        for (int j=i+1;j<=n;j++)
            if(g[i].c/g[i].e>g[j].c/g[j].e)
            swap(g[i],g[j]);
    for (int i=1;i<=n && var<e;i++)
    {
        while(var+g[i].e<e)
        {var+=g[i].e;
        cost+=g[i].c;}
    }
    h<<cost;
}
int main()
{
    citire();
    solve();
    return 0;
}