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.*; 

class Main{
public static void main(String[] args){
	Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        long m=sc.nextLong();
		long ans=0;

  		long[][] ab=new long[n][2];
		for(int c=0;c<n;c++){
    		ab[c][0]=sc.nextLong();
          	ab[c][1]=sc.nextLong();
    	}
  
        Arrays.sort(ab,(a, b) -> Long.compare(a[0], b[0]));
        long count=0;
        int c=0;
 		while(count<m){
        if(ab[c][1]>0){
        ans+=ab[c][0];
        ab[c][1]--;
        }else{
        ans+=ab[c+1][0];
        ab[c+1][1]--;
        c++;
        }
        count++;
        }

    	System.out.println(ans);
    }
}