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.*;
import java.math.BigInteger;

public class Main {

  public static void main(String[] args) { 
      Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int m = sc.nextInt();
      BigInteger cost = new BigInteger("0");
      int[][] arr = new int[n][2];
      for(int i = 0; i < n; i++) {
        arr[i][0] = sc.nextInt();
        arr[i][1] = sc.nextInt();
      }
      Arrays.sort(arr, (a1, a2) -> a1[0] - a2[0]);
      for(int i = 0; i < n && m > 0; i++) {
        long cnt = Math.min(arr[i][1], m);
        cost = cost.add(BigInteger.valueOf(cnt * arr[i][0]));
        m -= cnt;
      }
      System.out.println(cost.toString());
  }
}