/*
declare
i number:= 2;
j number;
status number:= 1;
total number:= 2;
num number := 3;

begin 
	while i<=10;
	loop
		j:=2;
		while j <= sqrt(num)
		loop
			if mod(num, j) = 0 
			then 
				status:=0;
				EXIT;
			end if;
			j:=j+1;
		end loop;
		if status = 1
		then 
			total:=total+num;
			i=:i+1;
		end if;
		status := 1;
		num:=num+1;
	end loop;
	dbmsoutput.putline(total);
end;






n number;
i number;
temp number;
counter number;
total number;
n:=2;
i:=2;
counter:=0;
temp:=1;

begin
	while counter < 11
	loop
		for i in 2..n/2
		loop
			if mod(n, i) = 0
			then 
				temp:=0;
				exit;
			end if;
		end loop;
		if temp = 1
		then
			counter:=counter+1;
			total:=total+n;
		end if;
		n:=n+1;
	end loop;
	dbms_output.put_line(total); 
end;
		

1,
11,
111,
1111,
11111,
111111,
1111111,
11111111,
111111111,
1111111111,
11111111111,
111111111111,
1111111111111,
11111111111111,
111111111111111,
1111111111111111,
11111111111111111,
111111111111111111,
1111111111111111111
*continous delovery, continous testing, continuous integration.
			
======================================================================
//support for network isolaion, use of snapshots
//testers and developers can share an itrace file to help reproducing and finding issues, allows you to examine the call staxk and local variables.
they are errors not picked up at testing, they are usually found in production.
small sizes, fast iteration.
//degrades application performace
//state preservation
//orchestrator, data protection manager.
//record some actions against the site
//build deploy, build deploy test, build only
analysis
//library
//firewall issues, missing data binding attributes.
//SCVMM tsting lab
//moniters via a "single pane of glass", itegrated with team foudation server
======================================================================
pair programming, delay building anything until required, frequent coummnication, unit testing.
test cases are developed before writing the code to pass them.
code changes to multiple files that are related to the same software change.
too many conflicting ideas
acquiring knowledge around business processes and using it.
proritzed and scheduled with input from the owner.
deliver more features and functionality, higher customer satisfaction, higher application quality, improved developer productivity.
prefers responding to change over following a plan.
processes.
to represent teams with diverse skills working together.
they are templets from which objects are instantiated.

=======================================================================
Graph and pattern workflow.
FTP
branch and merge
the default text editor opens and you enter a commmit message and save
git show master(merge conflicts)
gitignore(status of file)
git diff(review changes).
git branch hotfix(btanch called hotfix).
it's not free.
git branch -d hotfix(to remove a branch called hotfix).
git remote -v (remote with a git command).

//package B;

import java.util.Scanner;

public class B {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        while(t-->0) {
            int n = sc.nextInt();
            String s = sc.next();
            int leftDistance = 0;
            int rightDistance = 0;
            for(int i=0; i<n; i++)
                if(s.charAt(i) != '>') leftDistance++;
                else break;
            for(int i=n-1; i>=0; i--)
                if(s.charAt(i) != '<') rightDistance++;
                else break;
            System.out.println(Math.min(leftDistance, rightDistance));
        }
    }
}

//packagepackage C;

import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;
import java.util.TreeSet;

public class C {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt();
        HashMap<Integer, Integer> map = new HashMap<>();
        int bea[] = new int[n];
        long max = Long.MIN_VALUE;
        for(int i=0; i<n; i++) {
            int x = sc.nextInt();
            int y = sc.nextInt();
            map.put(y, x);
            bea[i] = y;
        }
        Arrays.sort(bea);
        for(int i=0; i<n; i++) {
            int j = i;
            int temp = 0;
            while(j <= (i+k-1) && j < n) {
                int t = map.get(bea[j]);
                temp += t;
                j++;
//                System.out.print(" t"+j+"= " + t);
            }
//            System.out.println();
            max = Math.max(max, (long) (bea[i] * temp));
        }
        System.out.println(max);
    }
}

*/
//package C;

import java.util.Arrays;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.TreeSet;

public class C {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt();
        int songs[][] = new int[n][2];
        for(int i=0; i<n; i++) {
            songs[i][0] = sc.nextInt();
            songs[i][1] = sc.nextInt();
        }
        Arrays.sort(songs, new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                return o1[1] - o2[1];
            }
        });
        PriorityQueue<Integer> lengths = new PriorityQueue<>();
        long pleasure = 0, length = 0;
        for(int i=n-1; i>=0; i--) {
            lengths.add(songs[i][0]);
            length += songs[i][0];
            if(lengths.size() > k) {
                length -= lengths.poll();
            }
            pleasure = Math.max(pleasure, songs[i][1]*length);
        }
        System.out.println(pleasure);
    }
}

