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.Map.Entry;
import java.util.Scanner;
import java.util.SortedMap;
import java.util.TreeMap;

public class Main {
	public static void main(String[] args) {
		Scanner reader = new Scanner(System.in);
		int N = reader.nextInt();
		int M = reader.nextInt();
		SortedMap<Long, Integer> AB = new TreeMap<Long, Integer>();
		long ans = 0;

		for (int i = 0; i < N; i++) {
			Long A= reader.nextLong();
			int B = reader.nextInt();
			if (AB.containsKey(A)) {
				AB.put(A, AB.get(A)+B);
			} else {
				AB.put(A, B);
			}
		}

		for (Entry<Long, Integer> entry : AB.entrySet()) {
			if (M <= 0) {
				break;
			} else {
				long key = entry.getKey();
				int value = entry.getValue();
				if (value > M) {
					ans += M * key;
					M = 0;
				} else {
					ans += value * key;
					M -= value;
				}
			}
		}
		System.out.print(ans);
		reader.close();
	}
}