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.ArrayList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int N = Integer.parseInt(line[0]);
		int M = Integer.parseInt(line[1]);
		
		ArrayList <Shop> al = new ArrayList<>();
		
		int[] A = new int[N];
		int[] B = new int[N];
		for(int i= 0;i<N;i++) {
			line = sc.nextLine().split(" ");
			al.add(new Shop(Integer.parseInt(line[0]),Integer.parseInt(line[1]))); 
		}
		sc.close();
		
		al.sort((s1,s2)-> s1.a - s2.a );
		
		long amount =0;
		for(Shop s:al) {
			if(s.b<M) {
				amount += (long)s.a*s.b;
				M -= s.b;
			}else {
				amount += (long)s.a*M;
				break;
			}
		}
		
		System.out.println(amount);

	}

}

class Shop{
	int a;
	int b;
	
	public Shop(int a, int b) {
		this.a = a;
		this.b = b;
	}
}