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 {
	Scanner sc = new Scanner(System.in);

	void doIt() {
		int N = sc.nextInt();
		int M = sc.nextInt();
		pInt[] drink = new pInt[N];
		for(int i = 0; i < N; i++) {
			drink[i] = new pInt(sc.nextInt(), sc.nextInt());
		}
		Arrays.sort(drink);
		long ans = 0;
		for(int i = 0; i < N; i++) {
			if(M > drink[i].cap) {
				ans += drink[i].cap * drink[i].cost;
				M -= drink[i].cap;
			}
			else {
				ans += M * drink[i].cost;
				System.out.println(ans);
				return;
			}
		}
	}
	
	class pInt implements Comparable<pInt>{
		long cost;
		long cap;
		pInt(long c, long n){
			cost = c;
			cap = n;
		}
		@Override
		public int compareTo(pInt arg0) {
			return (int)(this.cost - arg0.cost);
		}
		
		
	}
	
	public static void main(String[] args) {
		new Main().doIt();
	}
}