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.*;
class Drink {
    int cost;
    int amount;
    public Drink(int cost, int amount) {
	this.cost = cost;
	this.amount = amount;
    }

    public int getCost() {
	return this.cost;
    }
}
class Main {
    public static void main(String[] args) {
	Scanner sc = new Scanner(System.in);
	int N = Integer.parseInt(sc.next());
	int M = Integer.parseInt(sc.next());
	Drink[] drinks = new Drink[N];
	long yen = 0;
	for(int i = 0; i<N; i++) {
	    drinks[i] = new Drink(Integer.parseInt(sc.next()),Integer.parseInt(sc.next()));
	}
	Arrays.sort(drinks, Comparator.comparing(Drink::getCost));
	for(int i = 0; i<N; i++) {
	    if(drinks[i].amount<=M) {
		yen += (long)drinks[i].cost*(long)drinks[i].amount;
		M = M-drinks[i].amount;
	    }else{
		yen += (long)drinks[i].cost*(long)M;
		M = 0;
	    }
	    if(M<=0)break;
	}
	System.out.println(yen);
    }
}