Buggy python submission (verdict: Time Limit Exceeded):
import sys
from itertools import permutations, combinations, combinations_with_replacement, product

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(500000)

N, K, *A = map(int, read().split())
K_ = K
comb = list(combinations(A, 2))
comb = sorted(comb, key=lambda p: p[0] * p[1])

tmp = comb[K - 1]
print(tmp[0] * tmp[1])


Fixed submission:
import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(500000)


def count(x):
    cnt = 0
    if x >= 0:
        cnt += N * len(zero)
    cnt += np.searchsorted(A, x // pos, side='right').sum()
    cnt += N * len(neg) - np.searchsorted(A, -(-x // neg), side='left').sum()
    cnt -= np.count_nonzero(A * A <= x)

    return cnt // 2


N, K, *A = map(int, read().split())
A = np.array(A)
A.sort()

neg = A[A < 0]
zero = A[A == 0]
pos = A[A > 0]

r = 10**18
l = -r

while r - l > 1:
    m = (r + l) // 2
    if count(m) >= K:
        r = m
    else:
        l = m

print(r)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from itertools import permutations, combinations, combinations_with_replacement, product

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(500000)

N, K, *A = map(int, read().split())
K_ = K
comb = list(combinations(A, 2))
for i, p in enumerate(comb):
    comb[i] = (min(p), max(p))
comb = sorted(comb, key=lambda p: p[0] * p[1])

tmp = comb[K - 1]
print(tmp[0] * tmp[1])


Fixed submission:
import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(500000)


def count(x):
    cnt = 0
    if x >= 0:
        cnt += N * len(zero)
    cnt += np.searchsorted(A, x // pos, side='right').sum()
    cnt += N * len(neg) - np.searchsorted(A, -(-x // neg), side='left').sum()
    cnt -= np.count_nonzero(A * A <= x)

    return cnt // 2


N, K, *A = map(int, read().split())
A = np.array(A)
A.sort()

neg = A[A < 0]
zero = A[A == 0]
pos = A[A > 0]

r = 10**18
l = -r

while r - l > 1:
    m = (r + l) // 2
    if count(m) >= K:
        r = m
    else:
        l = m

print(r)

Buggy python submission (verdict: Runtime Error):
import sys
from itertools import permutations, combinations, combinations_with_replacement, product

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(500000)

N, K, *A = map(int, read().split())

ans = [0] * (N * (N - 1) // 2)
for i, p in enumerate(combinations(A, 2)):
    ans[i] = p[0] * p[1]

print(sorted(ans)[K - 1])


Fixed submission:
import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(500000)


def count(x):
    cnt = 0
    if x >= 0:
        cnt += N * len(zero)
    cnt += np.searchsorted(A, x // pos, side='right').sum()
    cnt += N * len(neg) - np.searchsorted(A, -(-x // neg), side='left').sum()
    cnt -= np.count_nonzero(A * A <= x)

    return cnt // 2


N, K, *A = map(int, read().split())
A = np.array(A)
A.sort()

neg = A[A < 0]
zero = A[A == 0]
pos = A[A > 0]

r = 10**18
l = -r

while r - l > 1:
    m = (r + l) // 2
    if count(m) >= K:
        r = m
    else:
        l = m

print(r)