#define LOCAL
#define _USE_MATH_DEFINES
#include <array>
#include <cassert>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <vector>
#include <queue>
#include <stack>
#include <list>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <algorithm>
#include <complex>
#include <cmath>
#include <numeric>
#include <bitset>
#include <functional>
#include <random>
#include <ctime>

using namespace std;

template <typename A, typename B>
ostream& operator <<(ostream& out, const pair<A, B>& a) {
  out << "(" << a.first << "," << a.second << ")";
  return out;
}
template <typename T, size_t N>
ostream& operator <<(ostream& out, const array<T, N>& a) {
  out << "["; bool first = true;
  for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]";
  return out;
}
template <typename T>
ostream& operator <<(ostream& out, const vector<T>& a) {
  out << "["; bool first = true;
  for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]";
  return out;
}
template <typename T, class Cmp>
ostream& operator <<(ostream& out, const set<T, Cmp>& a) {
  out << "{"; bool first = true;
  for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "}";
  return out;
}
#ifdef LOCAL
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...) 42
#endif
template <typename Arg1>
void __f(const char* name, Arg1&& arg1){
  cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args){
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << ": " << arg1 << " |";
  __f(comma + 1, args...);
}

typedef long long int64;
typedef pair<int, int> ii;
const int64 INF = 1LL << 60;
const int MOD = 1e9 + 7;
mt19937 mrand(random_device{}());
int rnd(int x) { return mrand() % x; }

struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
  };
} fast_ios_;

int main() {
  int64 n, m;
  scanf("%lld%lld", &n, &m);
  vector<int64> a(n);
  for (int i = 0; i < n; ++i) {
    scanf("%lld", &a[i]);
  }
  sort(a.begin(), a.end());
  // trace(a);
  int64 low = -INF, high = INF;
  while (low != high) {
    int64 mid = low + (high - low) / 2;
    // trace(low, high, mid);
    int64 cnt = 0;
    for (int i = 0; i < n; ++i) {
      if (a[i] == 0) {
        if (mid >= 0) cnt += n - 1;
      } else if (a[i] > 0) {
        int64 r = mid % a[i];
        if (r < 0) r += a[i];
        int64 R = (mid - r) / a[i];
        // trace(mid, a[i], R);
        cnt += upper_bound(a.begin(), a.end(), R) - a.begin();
        if (a[i] * a[i] <= mid) --cnt;
      } else {
        int64 r = (-mid) % (-a[i]);
        if (r < 0) r += -a[i];
        int64 L = (-mid + (-a[i] - r) % (-a[i])) / (-a[i]);
        // trace(mid, a[i], L);
        cnt += n - (lower_bound(a.begin(), a.end(), L) - a.begin());
        if (a[i] * a[i] <= mid) --cnt;
      }
      // trace(i, cnt);
    }
    cnt /= 2;
    if (cnt < m) {
      low = mid + 1;
    } else {
      high = mid;
    }
  }
  printf("%lld\n", high);
  return 0;
}


Measured memory_bytes: 1792