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();
		long m = sc.nextInt();
		Store[] stores = new Store[n];
		for(int i = 0;i < n;i ++) {
			int price = sc.nextInt(), max = sc.nextInt();
			stores[i] = new Store(price,max);
		}
		Arrays.sort(stores);
		long drinksum = 0, pricesum = 0,diff = 0;
		for(int i = 0;i < n;i ++) {
			Store s = stores[i];
			long max = Long.valueOf(s.max);
			long price = Long.valueOf(s.price);
			drinksum += max;
			if(drinksum > m) {
				diff = drinksum - m;
				pricesum += price * (max - diff);
				break;
			}else if (drinksum == m) {
				pricesum += price * max;
				break;
			}
			pricesum += price * max;
		}
		System.out.println(pricesum);
	}
}

class Store implements Comparable<Store>{
	int price;
	int max;
	
	public Store(int price,int max){
		this.price = price;
		this.max = max;
	}

	@Override
	public int compareTo(Store s) {
		return this.price - s.price;
	}
}