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 Map<Long, Long> map = new TreeMap<Long, Long>(); // key:金額,val:本数

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int M = sc.nextInt();

		for (int i = 0; i < N; i++) {
			long a = sc.nextInt();
			long b = sc.nextInt();
			if (map.containsKey(a)) {
				map.put(a, map.get(a) + b);
			} else {
				map.put(a, b);
			}
		}
		sc.close();

		long ans = 0;
		int cnt = 0;

		for (Map.Entry<Long, Long> en : map.entrySet()) {
			long price = en.getKey();
			long num = en.getValue();

			for (int i = 0; i < num; i++) {
				if (cnt < M) {
					ans += price;
					cnt++;
				} else {
					break;
				}
				}
		}

		System.out.println(ans);
	}
}