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.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int m = sc.nextInt();

		Shop[] shops = new Shop[n];

		for(int i = 0; i < n; i++){
			shops[i] = new Shop(sc.nextInt(), sc.nextInt());
		}

		Arrays.sort(shops);
		long total = 0;
		for(int i = 0; i < n; i++){
			if(shops[i].stock < m){
				total += (long)shops[i].stock*shops[i].price;
				m -= shops[i].stock;
			}
			else {
				total += (long)m*shops[i].price;
				break;
			}

//			System.out.println("total "+total+" m "+m);
		}

		System.out.println(total);
	}
}

class Shop implements Comparable<Shop>{
	int price;
	int stock;

	Shop(int price, int stock){
		this.price = price;
		this.stock = stock;
	}

	@Override
	public int compareTo(Shop s) {
		// TODO 自動生成されたメソッド・スタブ
		return this.price - s.price;
	}


}