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.*;

class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[][] ab = new int[n][2];
		for(int i = 0; i < n; i++){
			ab[i][0] = sc.nextInt();
			ab[i][1] = sc.nextInt();
		}
		Arrays.sort(ab,(a,b) -> Integer.compare(a[0],b[0]));
		long ans = 0;
		int ans2 = 0;
		int i = 0;
		while(ans2 != m){
			for(int j = 0; j < ab[i][1] && ans2!=m; j++){
				ans+=ab[i][0];
				ans2++;
			}
			i++;
		}
		System.out.print(ans);
	}
}