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.Map;
import java.util.Scanner;
import java.util.TreeMap;

public class Main {

  public static void main(String[] args) {
    try (Scanner sc = new Scanner(System.in);) {
      int N = sc.nextInt();
      int M = sc.nextInt();

      Map<Long, Long> tMap = new TreeMap<>();
      for (int i = 0; i < N; i++) {
        long price = sc.nextInt();
        long left = sc.nextInt();
        if (tMap.containsKey(price)) {
          tMap.put(price, tMap.get(price) + left);
        } else {
          tMap.put(price, left);
        }
      }

      long ans = 0;
      for (Map.Entry<Long, Long> entry : tMap.entrySet()) {
        long buy = Math.min(M, entry.getValue());
        ans += buy * entry.getKey();
        M -= buy;
        if(M <= 0) {
          break;
        }
      }

      System.out.println(ans);
    }
  }
}