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{
  static class Store implements Comparable<Store>{
    long price, cans;
    Store(long price, long cans){
      this.price = price;
      this.cans = cans;
    }
    public int compareTo(Store obj){
      if(this.price > obj.price){return 1;}
      if(this.price < obj.price){return -1;}
      return 0;
    }
  }
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    long N = sc.nextLong();
    long M = sc.nextLong();
    List<Store> stores = new ArrayList<>();
    for(int i=0; i<N; i++){
      stores.add(new Store(sc.nextLong(), sc.nextLong()));
    }
    Collections.sort(stores);
    long sum = 0;
    for(int i=0; i<N; i++){
      Store si = stores.get(i);
      if(si.cans < M){
        sum += si.price*si.cans;
        M -= si.cans;
      }else{
        sum += si.price*M;
        break;
      }
    }
    System.out.print(sum);
  }
}