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 {

    Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        new Main().run();
    }

    void run() {

        int n = sc.nextInt();
        int m = sc.nextInt();

        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, (x, y) -> x[0] - y[0]);

        long ret = 0;

        int sum = 0;
        for (int i=0; i<n; i++) {
            sum += arr[i][1];
            if (m <= sum) {
                ret += (long)(m + arr[i][1] - sum) * arr[i][0];
                break;
            } else {
                ret += (long)arr[i][1] * arr[i][0];
            }
        }

        System.out.println(ret);

    }


}