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.Scanner;
import java.util.TreeMap;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int N = scan.nextInt();
		int M = scan.nextInt();

		TreeMap<Long, Long> tm = new TreeMap<>();
		long cost = 0;

		for (int i = 0; i < N; i++) {
			long key = scan.nextLong();
			long value = scan.nextLong();
			if (tm.containsKey(key)) {
				tm.put(key, tm.get(key) + value);
			} else {
				tm.put(key, value);
			}
		}

		for (long i : tm.keySet()) {
			if (M <= tm.get(i)) {
				cost += i * M;
				break;
			} else {
				M -= tm.get(i);
				cost += i * tm.get(i);
			}
		}
		System.out.println(cost);
		
	}
}