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

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt(); //軒数
		
		int m = stdIn.nextInt(); //買う本数
		
		
		Map <Long, Long> map = new TreeMap<>();
		
		for(int i = 0; i < n; i++) {
			long a = stdIn.nextLong(); //値段
			long b = stdIn.nextLong(); //本数
			
			if(!map.containsKey(a)) {
				map.put(a, b);
			}else {
				map.put(a, map.get(a)+b);
			}
			
		}
		
		long ans = 0;
		
		for(long s: map.keySet()) {
			
			if(m <= map.get(s)) {
				ans += s * m;
				break;
			}else {
				ans += s * map.get(s);
				m -= map.get(s);
			}
			
			
			
		}
		
		System.out.println(ans);
		
	}

}