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;

class Pair implements Comparable<Pair>{
	int A, B;
	public Pair(int _A, int _B) {
		A = _A;
		B = _B;
	}
	public int compareTo(Pair o) {
		return A - o.A;
	}

}

public class Main {
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		int N = sc.nextInt(), M = sc.nextInt();
		Pair[] energy = new Pair[N];
		for(int i = 0; i < N; i++) {
			energy[i] = new Pair(sc.nextInt(), sc.nextInt());
		}
		Arrays.sort(energy);
		long cost = 0;
		for(int i = 0; i < N; i++) {
			if(M == 0) break;
			int buy = Math.min(energy[i].B, M);
			M -= buy;
			cost += (long)buy * (long)energy[i].A;
		}
		System.out.println(cost);
	}
}