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();
        long M = sc.nextLong();
        long count_opt =0;
        long price_opt =0;
        ArrayList<Drink> List = new ArrayList<>();
        for(int a=0;a<N;a++){
            long price = sc.nextLong();
            long count = sc.nextLong();
            Drink d = new Drink(price,count);
            List.add(d);
        }
        List.sort(Comparator.comparing(e -> e.price));
        for(Drink d:List){
            if(count_opt+d.count>=M){
                price_opt += (M-count_opt)*d.price;
                break;
            }
            count_opt+=d.count;
            price_opt+=d.count*d.price;
        }
        System.out.println(price_opt);
    }
}

class Drink{
    long price;
    long count;
    public Drink(final long price,final long count){
        this.price = price;
        this.count = count;
    }
}