Problem:
Score: 400 points

Problem Statement

We have N integers A_1, A_2, ..., A_N.

There are \frac{N(N-1)}{2} ways to choose two of them and form a pair. If we compute the product of each of those pairs and sort the results in ascending order, what will be the K-th number in that list?

Constraints

All values in input are integers.

2 \leq N \leq 2 \times 10^5

1 \leq K \leq \frac{N(N-1)}{2}

-10^9 \leq A_i \leq 10^9\ (1 \leq i \leq N)

Input

Input is given from Standard Input in the following format:

N K
A_1 A_2 \dots A_N

Output

Print the answer.

Sample Input 1

4 3
3 3 -4 -2

Sample Output 1

-6

There are six ways to form a pair. The products of those pairs are 9, -12, -6, -12, -6, 8.

Sorting those numbers in ascending order, we have -12, -12, -6, -6, 8, 9. The third number in this list is -6.

Sample Input 2

10 40
5 4 3 2 -1 0 0 0 0 0

Sample Output 2

6

Sample Input 3

30 413
-170202098 -268409015 537203564 983211703 21608710 -443999067 -937727165 -97596546 -372334013 398994917 -972141167 798607104 -949068442 -959948616 37909651 0 886627544 -20098238 0 -948955241 0 -214720580 277222296 -18897162 834475626 0 -425610555 110117526 663621752 0

Sample Output 3

448283280358331064

Solution in C (Clang 3.8.0) (judge verdict: Runtime Error)

#include<stdio.h>

int main (void){
  int N,K,num[200000],cnt=0,buf;
  int id;
  scanf("%d %d",&N,&K);
  while(N>cnt){
      scanf("%d",&num[cnt]);
      cnt ++;
  }
    int i,j,temp;

  for(i=0; i<N; i++){
    for(j=N-1; j>i; j--){
      if(num[j] < num[j-1]){
        temp = num[j];
        num[j] = num[j-1];
        num[j-1] = temp;
      }
    }
  }

  printf("%d",num[K]*num[K-1]);
  return 0;

}