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 s = new Scanner(System.in);
		
		int n = s.nextInt();
		int m = s.nextInt();
		
		long[][] cond = new long[n][2];
		
		long total = 0;
		long amount = 0;
		for(int i=0;i < n; i++) {
			cond[i][0] = s.nextInt();
			cond[i][1] = s.nextInt();
			
		}
		
		Arrays.sort(cond, (a, b) -> Long.compare(a[0], b[0]));
		
		for(long[] shop : cond) {
			for(int j=0;j<shop[1];j++) {
				total = total + shop[0];
				amount++;
				if(amount >=m) {
					System.out.println(total);
					return;
				}
			}
		}

	}

}