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 numShop = sc.nextInt();
		int numDrink = sc.nextInt();
		long sell[][] = new long[numShop][2];//price,max
		for(int i = 0; i < numShop; i ++) {
			sell[i][0] = sc.nextLong();
			sell[i][1] = sc.nextLong();
		}
		Arrays.sort(sell, (a, b) -> Long.compare(a[0], b[0]));
		long cost = 0;
		long rest = numDrink;
		for(int i = 0; i < numShop; i ++) {
			if(rest >= sell[i][1]) {
				cost += sell[i][0] * sell[i][1];
				rest -= sell[i][1];
			}else {
				cost += sell[i][0] * rest;
				break;
			}
		}
		System.out.println(cost);
	}
}