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.Collections;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        List<Element> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            list.add(new Element(a, b));
        }
        Collections.sort(list, (e1, e2) -> e1.a - e2.a);
        sc.close();

        long ans = 0;
        int needsNum = m;
        while (needsNum > 0) {
            Element e = list.remove(0);
            if (e.b <= needsNum) {
                ans += (long) e.a * (long) e.b;
                needsNum -= e.b;
            } else {
                ans += (long) e.a * (long) needsNum;
                needsNum = 0;
            }
        }
        System.out.println(ans);
    }

    static class Element {
        int a;
        int b;

        Element(int a, int b) {
            this.a = a;
            this.b = b;
        }
    }
}