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) {
		Main main = new Main();
		main.solve();
	}

	void solve() {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());//店の数
		int m = Integer.parseInt(sc.next());//買いたい本数
		long [][] a = new long[n][2];
		for(int i=0; i<n;i++) {
			a[i][0] = Long.parseLong(sc.next());
			a[i][1] = Long.parseLong(sc.next());
		}
		sc.close();

		Arrays.sort(a,(a1,a2)->Long.compare(a1[0],a2[0]));
		long cnt=0,sumYen=0;
		for(int i=0;i<n&&cnt<m;i++) {
			for(long j=a[i][1];cnt<m&&j>0;j--) {
				cnt++;
				sumYen+=a[i][0];
			}
			//System.out.println(a[i][0]+" "+a[i][1]);
		}
		System.out.println(sumYen);
	}
}