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.Comparator;
import java.util.List;
import java.util.Scanner;

public class Main {

    static class Drink {
        long a;
        int b;

        public Drink(long a, int b) {
            this.a = a;
            this.b = b;
        }

        public long getA() {
            return a;
        }

    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        List<Drink> drink = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            drink.add(new Drink(sc.nextLong(), sc.nextInt()));
        }
        long yen = 0;
        int count = 0;
        drink.sort(Comparator.comparing(Drink::getA));

        for (int i = 0; i < drink.size(); i++) {
            for (int j = 0; j < drink.get(i).b; j++) {
                yen += drink.get(i).a;
                count++;
                if (count >= m) {
                    System.out.println(yen);
                    return;
                }
            }
        }
    }

}