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.*;
public class Main{
  	public static void main(String[] args) {
		
		Scanner keyboard = new Scanner(System.in); 
		
		int N  = keyboard.nextInt();
		int M = keyboard.nextInt();
				
		int[][]drink = new int[N][2];
		for(int i=0; i<N; i++){
			for(int j=0; j<2; j++){
				drink[i][j] = keyboard.nextInt();
			}
		}
		Arrays.sort(drink, (l,r) -> {return l[0]-r[0];});
		
		int buy = M;
		long money = 0;
		for(int k=0; k<N; k++) {
			buy -= drink[k][1];
			if(buy > 0) {
				money += (long)drink[k][0]*drink[k][1];	
			}else{
				money += (long)drink[k][0]*(drink[k][1]+buy);
				break;
			}
		}
		
		System.out.println(money);
		keyboard.close();	
	}
}