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();
		Shop[] arr = new Shop[n];
		for (int i = 0; i < n; i++) {
		    arr[i] = new Shop(sc.nextInt(), sc.nextInt());
		}
		Arrays.sort(arr);
		long total = 0;
		for (Shop s : arr) {
		    total += Math.min(m, s.count) * (long)(s.cost);
		    m -= s.count;
		    if (m < 0) {
		        break;
		    }
		}
		System.out.println(total);
	}
	
	static class Shop implements Comparable<Shop> {
	    int cost;
	    int count;
	    
	    public Shop(int cost, int count) {
	        this.cost = cost;
	        this.count = count;
	    }
	    
	    public int compareTo(Shop s) {
	        return this.cost - s.cost;
	    }
	}
}