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) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m =  sc.nextInt();

        List<Store> storeList = new ArrayList<>(n);
        for (int i = 0; i < n; i++){
            long price = sc.nextLong();
            long amount = sc.nextLong();
            Store store = new Store(price, amount);
            storeList.add(store);
        }

        storeList.sort(Comparator.comparingLong(a -> a.price));

        long money = 0L;
        int drinkAmount = 0;
        for (Store store : storeList){
            if (drinkAmount + store.amount >= m){
                money += store.price * (m - drinkAmount);
                break;
            }
            money += store.price * store.amount;
            drinkAmount += store.amount;
        }

        System.out.println(money);
    }

    static class Store{
        long price;
        long amount;
        public Store(long p, long a){
            price = p;
            amount = a;
        }
    }

}