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.*;
import java.io.*;
import static java.lang.System.in;

public class Main {
    static int n,m,C;
    //static int[] A,B;
    static HashSet<Integer>[] graph;
    public static void main(String[] args)throws IOException {
        //BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt(); m = sc.nextInt();
        int[][] rec = new int[n][2];
        for(int i=0;i<n;i++){
            int a=sc.nextInt(), b=sc.nextInt();
            rec[i][0] = a; rec[i][1] = b;
        }
        Arrays.sort(rec,(a,b)->(a[0]-b[0])); // sort by price each
        long ans = 0, num = 0;
        for(int i=0;i<n;i++){
            long cur = Math.min(rec[i][1],m-num);
            ans += ((long)rec[i][0])*cur;
            num += cur;
            if(num==m) break;
        }
        System.out.println(ans);
    }
}