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.Arrays;
import java.util.Scanner;

public class Main {

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

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

		Shop[] shop=new Shop[N];

		for(int i=0;i<N;i++) {
			shop[i]=new Shop();
			shop[i].price=sc.nextLong();
			shop[i].stock=sc.nextInt();
		}

		Arrays.sort(shop);

		int now_Drink=0;
		int Drink_count=0;
		long ans=0;


		for (int i=0;i<N;i++){

			now_Drink=shop[i].stock;

			if(M < Drink_count+now_Drink) {
				now_Drink=(M-Drink_count);
			}

			ans+=(now_Drink*shop[i].price);
			Drink_count+=now_Drink;

			if(Drink_count==M) break;

        }

		System.out.println(ans);

		sc.close();
	}

}


class Shop implements Comparable<Shop>{
	Long price;
	int stock;

	@Override
	public int compareTo(Shop s) {
		long x=this.price-s.price;
		if(x > 0) return 1;
		else if(x == 0) return 0;
		else return -1;
	}
}