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.Map;
import java.util.Scanner;
import java.util.TreeMap;
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		long[][] cell = new long[n][2];
		for(int i = 0; i < n; i++) {
			cell[i][0] = sc.nextInt();
			cell[i][1] = sc.nextInt();
		}
		Arrays.sort(cell, (a, b) -> Long.compare(a[0], b[0]));
		long ans = 0;
		long cnt  = m;
		for(int i = 0; i < n; i++) {
			if(cnt >= cell[i][1]) {
				ans += cell[i][0] * cell[i][1];
				cnt -= cell[i][1];
			}else {
				ans += cell[i][0] * cnt;
				break;
			}
		}
		System.out.println(ans);
		sc.close();
	}
}