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) {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int m = sc.nextInt();
        ArrayList<Shop> list = new ArrayList<>();

        for (int i = 0; i < n; i++) {
            list.add(new Shop(sc.nextLong(), sc.nextInt()));
        }
        list.sort(Comparator.comparingLong(a -> a.value));

        long ans = 0;

        while (m > 0) {
            Shop target = list.get(0);
            list.remove(0);
            int kosu = Math.min(m, target.kosu);
            ans += target.value * kosu;
            m -= kosu;
        }

        System.out.println(ans);
    }

    public static class Shop {
        public long value;
        public int kosu;

        public Shop(long value, int kosu) {
            this.value = value;
            this.kosu = kosu;
        }
    }
}