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.Scanner;
import java.util.Arrays;

public class Main {
  public static void main (String[] args) {
    Scanner in = new Scanner(System.in);

    while (in.hasNext()) {
      int N = in.nextInt();
      int M = in.nextInt();
      Shop[] shop = new Shop[N];

      for (int i = 0; i < shop.length; ++i) {
        shop[i] = new Shop(in.nextInt(), in.nextInt());
      }
      
      Arrays.sort(shop);

      long cost = 0;
      for (int i = 0; M > 0; ++i) {
        cost += (long)shop[i].price * Math.min(M, shop[i].numOfDrink);
        M -= shop[i].numOfDrink;
      }

      System.out.println(cost);
    }
  }

  private static class Shop implements Comparable<Shop>{
    int price;
    int numOfDrink;
    
    Shop (int price, int numOfDrink) {
      this.price = price;
      this.numOfDrink = numOfDrink;
    }

    @Override
    public int compareTo(Shop s) {
      return this.price - s.price;
    }
  }
}