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.PriorityQueue;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

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

		PriorityQueue<Def> pq = new PriorityQueue<>();
		for(int i = 0; i < n; i++) {
			pq.add(new Def(sc.nextLong(), sc.nextInt()));
		}

		long ans = 0;
		while(true) {
			Def d = pq.poll();
			if(d.num >= m) {
				ans += d.price * m;
				break;
			}else {
				ans += d.price * d.num;
				m -= d.num;
			}
		}

		System.out.println(ans);
	}
}

class Def implements Comparable<Def> {
	long price;
	int num;

	Def(long price, int num) {
		this.price = price;
		this.num = num;
	}

	@Override
	public int compareTo(Def d) {
		if(price < d.price) return -1;
		if(price == d.price) return 0;
		return 1;
	}
}