Problem: Hearing that energy drinks increase rating in those sites, Takahashi decides to buy up M cans of energy drinks.

There are N stores that sell energy drinks. In the i-th store, he can buy at most B_i cans of energy drinks for A_i yen (the currency of Japan) each.

What is the minimum amount of money with which he can buy M cans of energy drinks?

It is guaranteed that, in the given inputs, a sufficient amount of money can always buy M cans of energy drinks.

Constraints

* All values in input are integers.
* 1 \leq N, M \leq 10^5
* 1 \leq A_i \leq 10^9
* 1 \leq B_i \leq 10^5
* B_1 + ... + B_N \geq M

Input

Input is given from Standard Input in the following format:


N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N


Output

Print the minimum amount of money with which Takahashi can buy M cans of energy drinks.

Examples

Input

2 5
4 9
2 4


Output

12


Input

4 30
6 18
2 5
3 10
7 9


Output

130


Input

1 100000
1000000000 100000


Output

100000000000000

Solution (in JAVA):

Solution:
import java.util.*;

public class Main {
    public static void main(String[] args) {    
        Scanner sc=new Scanner(System.in);
      ArrayList<Oder<Integer>>po=new ArrayList<>(); 
      int n=sc.nextInt();
      int m=sc.nextInt();
      for(int i=0;i<n;i++)
      po.add(new Oder<Integer>(sc.nextInt(),sc.nextInt()));
      Collections.sort(po,new Comparator<Oder<Integer>>() {
			public int compare(Oder<Integer> a,Oder<Integer> b) {
				return a.cont.compareTo(b.cont);
			}
		});
		long ans=0;
		for(int i=0;i<m;i++){
		    if(po.get(0).weight==0){
		        po.remove(0);
		        ans+=po.get(0).cont;
		        po.get(0).weight--;
		    }
		    else {
		        ans+=po.get(0).cont;
		        po.get(0).weight--;
		    }
		}
      System.out.println(ans);
    }
}
class Oder<T>{
	public T cont;
	public int weight;
	public Oder(T t) {
		this.cont =t;
	}
	public Oder(T t,int w) {
		cont =t;
		weight=w;
	}
	public String toString() {
		return cont.toString()+":"+weight;
	}
}