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.*;
import java.io.*;
public class Main{
    public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		Map<Long , Long> tm = new TreeMap<Long , Long>();
		int n = Integer.parseInt(sc.next());
		long m = Long.parseLong(sc.next());
		long a = 0;
		long b = 0;
		for(int i = 0 ; i < n ; i++){
			a = Long.parseLong(sc.next());
			b = Long.parseLong(sc.next());
			if(tm.containsKey(a)){
				tm.put(a , b + tm.get(a));
			}else{
				tm.put(a , b);
			}
		}
		sc.close();
		long yono = 0;
		for(long i : tm.keySet()){
			yono += i * tm.get(i);
			m -= tm.get(i);
			if(m <= 0){
				yono += i * (long)m;
				break;
			}
		}
		ou.print(yono + "\n");
		ou.flush();
    }
}