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();
        long ans=0;
        Map <Long,Long>map=new TreeMap<>();
        for(int i=0;i<n;i++){
            long a=sc.nextLong();
            long b=sc.nextLong();
            if(map.get(a)!=null){
                map.put(a,b+map.get(a));
            }else{
                map.put(a,b);
            }
        }
        for(long key:map.keySet()){
            if(map.get(key)<=m){
                ans+=key*map.get(key);
                m-=map.get(key);
            }else{
                ans+=key*m;
                break;
            }
        }
        System.out.println(ans);

    }
}