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.*;
import java.lang.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		ArrayList<KeySort> list = new ArrayList<>();
		for (int i = 0; i < n; i++) {
			long a = sc.nextLong();
			int b = sc.nextInt();
			list.add(new KeySort(b, a));
		}
		Collections.sort(list, new KeySortComparator());
		long money = 0;
		for (int i = 0; i < n; i++) {
			if (list.get(i).key <= m) {
				money += list.get(i).key * list.get(i).sort;
				m -= list.get(i).key;
			} else {
				money += m * list.get(i).sort;
				break;
			}
		}
		System.out.println(money);
	}
}
class KeySort {
	public int key;
	public long sort;
	public KeySort(int key, long sort) {
		this.key = key;
		this.sort = sort;
	}
}

class KeySortComparator implements Comparator<KeySort> {
	@Override
	public int compare(KeySort sort1, KeySort sort2) {
		if (sort1.sort == sort2.sort) {
			return 0;
		} else if (sort1.sort > sort2.sort) {
			return 1;
		} else {
			return -1;
		}
	}
}