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 long cost = 0;
  private int a;
  private int b;

  Main(int a, int b){
    this.a = a;
    this.b = b;
  }
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int m = sc.nextInt();

    Main[] d = new Main[n];

    for(int i=0; i<n; i++){
      d[i] = new Main(sc.nextInt(),sc.nextInt());
    }
    //for(int i=0; i<n; i++){
      //System.out.println(d[i].a+","+d[i].b);
    //}
    Arrays.sort(d,new Comparator<Main>(){
      public int compare(Main o1,Main o2){
        return o1.a - o2.a;
      }
    });
    //for(int i=0; i<n; i++){
      //System.out.println(d[i].a+","+d[i].b);
    //}
    int j = 0;
    while(m>0){
      if(m-d[j].b>=0){
        cost += (long)d[j].a * (long)d[j].b;
        m -=  d[j].b;
      }else if(m-d[j].b<0){
        cost += (long)d[j].a * (long)m;
        m = 0;
      }
      j++;

    }
    System.out.println(cost);


  }

}