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.math.BigInteger;
import java.util.*;
import java.util.TreeMap;

class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int shopNum = sc.nextInt();
		int drinkNum = sc.nextInt();
		Map<Integer, Integer> drinks = new TreeMap<>();
		for(int i = 0; i < shopNum; i++){
			int key = sc.nextInt();
			try {
				int prev = drinks.get(key);
				drinks.put(key, sc.nextInt()+prev);
			}catch(Exception e) {
				drinks.put(key, sc.nextInt());
			}
		}

		BigInteger ans = BigInteger.ZERO;
		for(Map.Entry<Integer, Integer> entry : drinks.entrySet()) {
			if(drinkNum > entry.getValue()) {
				drinkNum -= entry.getValue();
				ans = ans.add(new BigInteger(entry.getKey().toString()).multiply(new BigInteger(entry.getValue().toString())));
			}else {
				ans = ans.add(new BigInteger(String.valueOf(drinkNum)).multiply(new BigInteger(entry.getKey().toString())));
				break;
			}
		}
		System.out.println(ans);
	}
}