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:
//2019/3/12
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();

		long[][] AB = new long[N][2];

		long A,B;

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

				A = sc.nextLong();

				AB[i][0] = A;

				B = sc.nextLong();

				AB[i][1] = B;
		}

		Arrays.parallelSort(AB,(a,b) -> Long.compare(a[0],b[0]));

		long ans = 0;

		long x = 0;

		int index = 0;

		while(x<M) {

			if(x+AB[index][1]<=M) {

				ans += (AB[index][0]*AB[index][1]);

				x += AB[index][1];

			}else {

				for(int i=0;x<M;i++) {

					ans += AB[index][0];

					x++;

				}

			}

			index++;
		}

		System.out.println(ans);
	}

}