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.Arrays;
import java.util.Scanner;


public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int N = Integer.parseInt(sc.next());
		int M = Integer.parseInt(sc.next());
		long[][] A = new long[N][2];
		for(int i=0;i<N;i++){
			A[i][0] = Integer.parseInt(sc.next());
			A[i][1] = Integer.parseInt(sc.next());
		}
		Arrays.sort(A, (a, b) -> Long.compare(a[0], b[0]));
		int needBuy = M;
		long ans = 0;
		int count = 0;
		while(needBuy > 0){
			if(needBuy <= A[count][1]){
				ans += needBuy*A[count][0]; 
				needBuy = 0;
			}
			if(needBuy > A[count][1]){
				ans += A[count][1]*A[count][0]; 
				needBuy -= A[count][1];
				count++;
			}
		}
		
		System.out.println(ans);
		sc.close();
	}
	

}