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 = sc.nextInt();
        int M = sc.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int[][] C = new int[N][2];
        int sum = 0;
        for (int i = 0; i < N; i++) {
            A[i] = sc.nextInt();
            B[i] = sc.nextInt();
            sum += B[i];
            C[i][0] = A[i];
            C[i][1] = B[i];
        }
        sc.close();
        Arrays.sort(C, (a, b) -> Integer.compare(a[0], b[0]));
        long ans = 0;
        long tmp = M;
        for (int i = 0; i < M; i++) {
            if (C[i][1] < tmp) {
                tmp -= C[i][1];
                ans += (long)C[i][0] * (long)C[i][1];
            } else {
                ans += C[i][0] * tmp;
                break;
            }
        }
        System.out.println(ans);
    }
}