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;
import java.util.Scanner;
import java.util.TreeMap;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();	//軒数
		int M = sc.nextInt();	//ほしい本数
		long[] a = new long[N];
		long[] b = new long[N];


		Map<Long, Long> tMap = new TreeMap<Long, Long>();
		for (int i = 0; i < N; i++) {
			a[i] = sc.nextInt();
			b[i] = sc.nextInt();
			if(tMap.containsKey((a[i]))) {
				tMap.put((a[i]), tMap.get(a[i]) + b[i]);
			} else {
				tMap.put(a[i], b[i]);
			}
		}

		long ans = 0;
		for(Map.Entry<Long, Long> entry : tMap.entrySet()) {
			long buy = Math.min(M, entry.getValue());

			ans += buy * entry.getKey();

			M -= buy;
		}

		System.out.println(ans);

		sc.close();
	}
}