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[] A = new long[N],
               B = new long[N];
        List<long[]> al = new ArrayList<>();
        for(int i = 0; i < N; i++){
            A[i] = sc.nextLong();
            B[i] = sc.nextLong();
            al.add(new long[]{A[i], B[i]});
        }
        al.sort(Comparator.comparing(x -> x[0]));   
        int shop = 0;
        long money = 0;
        while(true){
            long stock = al.get(shop)[1],
                 price = al.get(shop)[0];
            if(stock < M){
                money += price*stock;
                M -= stock;
                shop++;
            }
            else{
                money += price*M;
                break;
            }
        }
        System.out.println(money);
    }
}