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 sc = new Scanner(System.in);

		int N = sc.nextInt();
		int M = sc.nextInt();

		TreeMap<Long, Integer> map = new TreeMap<>();
			for(int i = 0 ; i < N ; i++){
				long cost = sc.nextLong();
				int num = sc.nextInt();
				//map.put(cost,num);
				//map.put(cost,map.containsKey(cost)?num+map.get(cost):num);

				if(map.containsKey(cost)){
					map.put(cost,num + map.get(cost));
				}else{
					map.put(cost,num);
				}


				//map.compute(cost, (k,v) -> v==null? num : num+v);
			}
			sc.close();


			long totalcost = 0;
			int bought = 0;

			for(Map.Entry<Long,Integer> kv : map.entrySet()){
				long cost = kv.getKey();
				int maxnum = kv.getValue();

				int buycount = Math.min(maxnum, M-bought);
				totalcost += buycount * cost;
				bought += buycount;

				if(bought > M){
					break;
				}
			}
			System.out.println(totalcost);
	}

}