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.ArrayList;
import java.util.Comparator;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc  = new Scanner(System.in);
		int N = sc.nextInt();
		int M = sc.nextInt();
		ArrayList<int[]> data = new ArrayList<int[]>();
		
		long result = 0;
		boolean flag = true;
		
		for(int i = 0; i < N; i++) {
			int[] input = new int[2];
			input[0] = sc.nextInt();
			input[1] = sc.nextInt();
			data.add(input);
		}
		data.sort((a,b) -> Integer.compare(a[0],b[0]));
		
		int i = 0;
		int count_m = 0;
		int count = 0;
		
		while(M != count_m) {
			result += data.get(i)[0];
			count++;
			count_m++;
			
			int next_i = count/data.get(i)[1];
			count = count%data.get(i)[1];
			i += next_i;
		}
		System.out.println(result);
	}
}