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 scn = new Scanner(System.in);
    int N = scn.nextInt();
    int M = scn.nextInt();

    ArrayList<Data> data = new ArrayList<>();
    for (int i = 0; i < N; i++) {
      int A = scn.nextInt();
      int B = scn.nextInt();
      data.add(new Data(A, B));
    }

    Collections.sort(data, new Comparator<Data>() {
      public int compare(Data d1, Data d2) {
        return Long.compare(d1.price, d2.price);
      }
    });

    long expense = 0;
    int drinkCount = 0;
    for (Data d : data) {
      drinkCount += d.stock;
      expense += d.stock * d.price;

      if (drinkCount >= M) {
        int excess = drinkCount - M;
        expense -= excess * d.price;
        break;
      }
    }

    System.out.println(expense);
  }

  public static class Data {
    private long price;
    private int stock;

    Data(long a, int b) {
      this.price = a;
      this.stock = b;
    }
  }

}