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.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;

public class Main {

	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		long n=sc.nextLong();
		long m= sc.nextLong();
		long l=0;
		long price=0;
		Map<Long,Long> map = new HashMap<>();
		for(int i=0;i<n;i++) {
				long key= sc.nextLong();
				long value = sc.nextLong();
				if(map.containsKey(key)) {
			map.put(key,value+map.get(key));
				}else {
					map.put(key,value);
				}
		}
		List<Long> sortedKeys = new ArrayList(map.keySet());
		Collections.sort(sortedKeys);
	
		for( long nkey: sortedKeys) {
			long k=map.get(nkey);
			m-=k;
			if(m>0) {
			l+=k*nkey;
			}else{
				l+=nkey*(m+k);
				System.out.println(l);
				break;
			}


		}
    }

}