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 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next()); // 店数
        int M = Integer.parseInt(sc.next()); // 買いたい数
        Map<Long, Integer> map = new TreeMap<Long, Integer>();
 
        for (int i = 0; i < N; i++) {
            Long A = sc.nextLong();
            int B = sc.nextInt();
            if(map.containsKey(A)){
                map.put(A,map.get(A)+B);
            }else{
                map.put(A,B);
            }
        }
        Long sum = 0L;
        // int j = 0;
        loop: for(Long a: map.keySet()){
            int tmp = map.get(a);
            if(tmp>= M){
                sum += M*a;
                break loop;
            }else{
                sum += tmp*a;
                M -= tmp;
            }
        }
        System.out.print(sum);
    }
}