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.Comparator;
import java.util.Scanner;

class Problem {
    private int N;
    private int M;
    private Long[][] shops;

    Problem() {
        Scanner sc = new Scanner(System.in);

        N = sc.nextInt();
        M = sc.nextInt();

        shops = new Long[N][2];

        for (int i = 0; i < N; i++){
            shops[i][0] = sc.nextLong();
            shops[i][1] = sc.nextLong();
        }
    }

    long solve() {
        Arrays.sort(shops, new Comparator<Long[]>() {
            @Override
            public int compare(Long[] o1, Long[] o2) {
                return Long.compare(o1[0], o2[0]);
            }
        });

        long ans = 0;
        long m = M;
        int i = 0;
        while (m > 0) {
            long n = Math.min(shops[i][1], m);
            ans += shops[i][0] * n;
            m -= n;
            i++;
        }
        return ans;
    }
}

public class Main {
    public static void main(String[] args) {
        System.out.println(new Problem().solve());
    }
}