output_description: Print the answer.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N K
      A_1 A_2 \dots A_N
attempt: # from itertools import *
  
  
  class Combination:
      """
      O(n)の前計算を1回行うことで，O(1)でnCr mod mを求められる
      n_max = 10**6のとき前処理は約950ms (PyPyなら約340ms, 10**7で約1800ms)
      使用例：
      comb = Combination(1000000)
      print(comb(5, 3))  # 10
      """
  
      def __init__(self, n_max, mod=10**9 + 7):
          self.mod = mod
          self.modinv = self.make_modinv_list(n_max)
          self.fac, self.facinv = self.make_factorial_list(n_max)
  
      def __call__(self, n, r):
          return self.fac[n] * self.facinv[r] % self.mod * self.facinv[n - r] % self.mod
  
      def make_factorial_list(self, n):
          # 階乗のリストと階乗のmod逆元のリストを返す O(n)
          # self.make_modinv_list()が先に実行されている必要がある
          fac = [1]
          facinv = [1]
          for i in range(1, n + 1):
              fac.append(fac[i - 1] * i % self.mod)
              facinv.append(facinv[i - 1] * self.modinv[i] % self.mod)
          return fac, facinv
  
      def make_modinv_list(self, n):
          # 0からnまでのmod逆元のリストを返す O(n)
          modinv = [0] * (n + 1)
          modinv[1] = 1
          for i in range(2, n + 1):
              modinv[i] = self.mod - self.mod // i * modinv[self.mod % i] % self.mod
          return modinv
  
  
  n, k = map(int, input().split())
  a = list(map(int, input().split()))
  
  c = Combination(1000000)
  # c = list(combinations(a, 2))
  p = []
  
  for i in range(len(c)):
      p.append(c[i][0] * c[i][1])
  
  p.sort()
  
  print(p[k - 1])
  
problem_description: 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?
samples: [{"input": "4 3\n    3 3 -4 -2", "output": "-6\n    \n\nThere are six ways to form a pair. The products of those pairs are 9, -12, -6,\n-12, -6, 8.\n\nSorting those numbers in ascending order, we have -12, -12, -6, -6, 8, 9. The\nthird number in this list is -6.\n\n* * *"}, {"input": "10 40\n    5 4 3 2 -1 0 0 0 0 0", "output": "6\n    \n\n* * *"}, {"input": "30 413\n    -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", "output": "448283280358331064"}]