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.*;
import java.util.stream.*;

public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int N = in.nextInt();
    int M = in.nextInt();
    Pair[] p = new Pair[N];
    for (int i = 0; i < N; i++) {
      p[i] = new Pair(in.nextInt(), in.nextInt());
    }
    Arrays.sort(p, (s, t) -> s.a - t.a);
    long ans = 0;
    for (int i = 0; i < N; i++) {
      long cnt = Math.min(M, p[i].b);
      ans += (long) p[i].a * cnt;
      M -= (int) cnt;
      if (M == 0) {
        break;
      }
    }
    System.out.println(ans);
  }
}

class Pair {
  int a, b;

  public Pair(int a, int b) {
    this.a = a;
    this.b = b;
  }
}