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<Pair<Integer, Integer>> list = new ArrayList<Pair<Integer, Integer>>(); 
        
        for(int i = 0; i < n; i++){
            list.add(new Pair<Integer,Integer>(sc.nextInt(),sc.nextInt()));
        }
        
        list.sort((a,b) -> a.getKey() - b.getKey());
        
        long res = 0;
        
        for(Pair<Integer,Integer> pair : list){
            if(pair.getValue() <= m){
                m-=pair.getValue();
                res+=(long) pair.getKey() * (long) pair.getValue();
            }else{
                res+=(long) pair.getKey() * (long) m;
                break;
            }
        }
        
        System.out.println(res);
    }
}

class Pair<K, V> extends AbstractMap.SimpleEntry<K, V> {
    
    public Pair(final K key, final V value) {
        super(key, value);
    }
 }