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.Map;
import java.util.Scanner;
import java.util.TreeMap;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();

        TreeMap<Integer,Integer> map = new TreeMap<>();

        for (int i = 0; i < N; i++) {
            int price = sc.nextInt();
            int inv = sc.nextInt();
            if(!map.containsKey(price)){
                map.put(price,inv);
            }else{
                int val =  map.get(price);
                map.put(price,val+inv);
            }
        }

        long cost = 0;
        for(Map.Entry<Integer,Integer> e : map.entrySet()){
            int price = e.getKey();
            int num = e.getValue();
            if(num >= M){
                cost += (long)M * price;
                break;
            }else{
                cost += (long)price * num;
                M -= num;
            }
        }
        System.out.println(cost);
    }}