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 sc = new Scanner(System.in);
    long n = sc.nextLong();
    long m = sc.nextLong();
    SortedSet<Shop> shops = new TreeSet<>();
    for (int i = 0; i < n; i++) {
      long value = sc.nextLong();
      long limit = sc.nextLong();
      shops.add(new Shop(value, limit));
    }
    long cost = 0;
    for (Shop shop : shops) {
      if (m == 0) break;
      if (m >= shop.limit) {
        cost += shop.cost * shop.limit;
        m -= shop.limit;
      } else {
        cost += shop.cost * m;
        m = 0;
      }
    }
    System.out.println(cost);
  }

  static class Shop implements Comparable<Shop> {
    private long cost;
    private long limit;

    public Shop(long cost, long limit) {
      this.cost = cost;
      this.limit = limit;
    }

    @Override
    public int compareTo(Shop shop) {
      if (this.cost == shop.cost) {
        return 1;
      } else {
        return (int) (this.cost - shop.cost);
      }
    }
  }
}