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);
		int n = sc.nextInt();
		int m = sc.nextInt();
		Store[] arr = new Store[n];
		for (int i = 0; i < n; i++) {
			arr[i] = new Store(sc.nextInt(), sc.nextInt());
		}
		Arrays.sort(arr, new Comparator<Store>() {
		public int compare(Store s1, Store s2) {
			return s1.a - s2.a;
		}
		});
		long total = 0;
		for (int i = 0; i < n && m > 0; i++) {
			int amount = Math.min(arr[i].b, m);
			total += (long)amount * arr[i].a;
			m -= amount;
		}
		System.out.println(total);
	}
	
	static class Store {
		int a;
		int b;
		public Store(int a, int b) {
			this.a = a;
			this.b = b;
		}
	}
}