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.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long n = sc.nextInt();
        long m = sc.nextInt();
        List<int[]> kingakuq = new ArrayList<>();

        for (int i = 0; i < n; i++){
            int a = sc.nextInt();
            int b = sc.nextInt();
            kingakuq.add(new int[]{a, b});
        }

        kingakuq = kingakuq.stream().sorted((a,b) -> a[0] - b[0]).collect(Collectors.toList());
        long sum = 0;
        int index = 0;
        while (true) {
            if (m <= 0) break;
            long syou = (long)(kingakuq.get(index)[0]);
            long hon = (long)(kingakuq.get(index)[1]);
            if (hon <= m) {
                m -= hon;
                sum += syou * hon;
            } else {
                sum += syou * m;
                m = 0;
            }
            index++;
        }
        System.out.println(sum);
    }

}