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();
		int M = sc.nextInt();
		int[] A = new int[N];
		int[] B = new int[N];
		Map<Integer, Integer> map = new TreeMap<>();
		for(int i = 0;i < N;i++) {
			A[i] = sc.nextInt();
			B[i] = sc.nextInt();
			if(map.get(A[i])!=null) {
				map.put(A[i], B[i]+map.get(A[i]));
			}else {
				map.put(A[i], B[i]);
			}
		}
		sc.close();
		long sumKey = 0;
		long sumValue = 0;
		for(Map.Entry<Integer, Integer> entry : map.entrySet()) {
			for(int i = 0;i < entry.getValue();i++) {
				sumKey += entry.getKey();
				sumValue++;
				if(sumValue == M) {
					System.out.println(sumKey);
					return;
				}
			}
		}
	}
}