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:
// Arrays.sortの第二引数にコンパレータを定義した場合
// 参考 -> #4529481

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();
        int[][] AB = new int[n][2];

        for (int i = 0; i < n; i++) {
            AB[i][0] = sc.nextInt();
            AB[i][1] = sc.nextInt();
        }

        Arrays.sort(AB, (x, y) -> Integer.compare(x[0], y[0]));

        long totalPrice = 0;
        int totalCnt = 0;
        for (int i = 0; i < n; i++) {
            long price = AB[i][0];
            int count = AB[i][1];

            if (count >= m - totalCnt) {
                totalPrice += (m - totalCnt) * price;
                break;
            } else {
                totalPrice += count * price;
                totalCnt += count;
            }
        }

        System.out.println(totalPrice);
    }
}