// --------------------------------------------------<TEMPLATE>--------------------------------------------------
// --------------------<optimizations>--------------------
#pragma GCC optimize("O3")
//(UNCOMMENT WHEN HAVING LOTS OF RECURSIONS)\
#pragma comment(linker, "/stack:200000000")
//(UNCOMMENT WHEN TRYING TO BRUTEFORCE WITH A LOT OF LOOPS)\
#pragma GCC optimize("unroll-loops")
 
// -------------------</optimizations>--------------------
 
// ---------------<Headers and namespaces>----------------
#include <algorithm>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <ratio>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
 
// -----------------<Defines and typedefs>----------------
 
typedef long long ll;
typedef long double LD;
#define int ll
#define double LD
#define pb push_back
#define mp make_pair
#define loop(i,n) for (int i = 0; i < n; i++)
#define FOR(i,a,b) for (int i = a; i < b; i++)
#define REPD(i,n) for (int i = n-1; i >= 0; i--)
#define FORD(i,a,b) for (int i = a; i >= b; i--)
#define remax(a,b) a = max(a,b)
#define remin(a,b) a = min(a,b)
#define mem(a, b) memset(a, b, sizeof a)
#define append push_back
#define all(v) v.begin(),v.end()
typedef map<int,int> mii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
typedef vector<pii> vpii;
#define F first
#define S second
#define PQ(type) priority_queue<type>
#define PQD(type) priority_queue<type,vector<type>,greater<type> >
#define ITR :: iterator it
#define WL(t) while(t --)
#define SZ(x) ((int)(x).size())
#define TR(container,it) for(typeof(container.begin()) it=container.begin();it!=container.end();it++)
#define sqr(x) ((x)*(x))
 
// -----<SCANF>-----
#define sfi(x) scanf("%d",&x);
#define sfi2(x,y) scanf("%d%d",&x,&y);
#define sfi3(x,y,z) scanf("%d%d%d",&x,&y,&z);
 
#define sfl(x) scanf("%lld",&x);
#define sfl2(x,y) scanf("%lld%lld",&x,&y);
#define sfl3(x,y,z) scanf("%lld%lld%lld",&x,&y,&z);
 
#define sfs(x) scanf("%s",x);
#define sfs2(x,y) scanf("%s%s",x,y);
#define sfs3(x,y,z) scanf("%s%s%s",x,y,z);
// ----</SCANF>-----
 
// ----<PRINTF>-----
#define pfi(x) printf("%d\n",x);
#define pfi2(x,y) printf("%d %d\n",x,y);
#define pfi3(x,y,z) printf("%d %d %d\n",x,y,z);
 
#define pfl(x) printf("%lld\n",x);
#define pfl2(x,y) printf("%lld %lld\n",x,y);
#define pfl3(x,y,z) printf("%lld %lld %lld\n",x,y,z);
 
#define pfs(x) printf("%s\n",x);
#define pfs2(x,y) printf("%s %s\n",x,y);
#define pfs3(x,y,z) printf("%s %s %s\n",x,y,z);
// ----</PRINTF>----
 
#define FLSH fflush(stdout)
#define fileIO(name) \
    freopen(name".in", "r", stdin); \
    freopen(name".out", "w", stdout);
#define PRECISION(x) cout << fixed << setprecision(x)
#define FAST_IO ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
 
// ----------------</Defines and typedefs>----------------
 
// -------------------<Debugging stuff>-------------------
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1>void __f(const char* name, Arg1&& arg1){cout<<name<<" : "<<arg1<<"\n";}
template <typename Arg1, typename... Args>void __f(const char* names, Arg1&& arg1, Args&&... args)
{const char* comma=strchr(names+1,',');cout.write(names,comma-names)<<" : "<<arg1<<" , ";__f(comma+1, args...);} 
#define traceloop(x,a) { cerr<<#a<<": "; for(ll ix=0;ix<x;ix++) cerr<<a[ix]<<" "; cerr<<endl; }
 
// ------------------</Debugging stuff>-------------------
 
// ------------------------<Consts>-----------------------
const int SQRTN = 1003;
const int LOGN = 22;
const double PI=acos(-1);
const int INF = 1000000000;
const int MOD = 1000000007;
const int FMOD = 998244353;
const double eps = 1e-9;
 
// -----------------------</Consts>-----------------------
 
// -------------------------<RNG>-------------------------
mt19937 RNG(chrono::steady_clock::now().time_since_epoch().count()); 
#define SHUF(v) shuffle(all(v), RNG);
// Use mt19937_64 for 64 bit random numbers.
 
// ------------------------</RNG>-------------------------
 
// -----------------<Modular Arithmetic>------------------
template<typename T> T gcd(T a, T b){return(b?__gcd(a,b):a);}
template<typename T> T lcm(T a, T b){return(a*(b/gcd(a,b)));}
int add(int a, int b, int c){int res=a+b;return(res>=c?res-c:res);}
int mod_neg(int a, int b, int c){int res;if(abs(a-b)<c)res=a-b;else res=(a-b)%c;return(res<0?res+c:res);}
int mul(int a, int b, int c){ll res=(ll)a*b;return(res>=c?res%c:res);}
ll mulmod(ll a,ll b, ll m){ll q = (ll)(((LD)a*(LD)b)/(LD)m);ll r=a*b-q*m;if(r>m)r%=m;if(r<0)r+=m;return r;}
template<typename T>T expo(T e, T n){T x=1,p=e;while(n){if(n&1)x=x*p;p=p*p;n>>=1;}return x;}
template<typename T>T power(T e, T n, T m){T x=1,p=e;while(n){if(n&1)x=mul(x,p,m);p=mul(p,p,m);n>>=1;}return x;}
template<typename T>T extended_euclid(T a, T b, T &x, T &y){T xx=0,yy=1;y=0;x=1;while(b){T q=a/b,t=b;b=a%b;a=t;\
t=xx;xx=x-q*xx;x=t;t=yy;yy=y-q*yy;y=t;}return a;}
template<typename T>T mod_inverse(T a, T n){T x,y,z=0;T d=extended_euclid(a,n,x,y);return(d>1?-1:mod_neg(x,z,n));}
 
// -----------------</Modular Arithmetic>-----------------
// --------------------------------------------------</TEMPLATE>--------------------------------------------------
 
void solve();
 
signed main(){
    PRECISION(10);
    FAST_IO;
    int t = 1;
    // (UNCOMMENT FOR MULTIPLE TEST CASES) \
    sfi(t);
    FOR(testcase,1,t+1){
        // (UNCOMMENT FOR CODEJAM) \
        printf("Case #%lld: ",testcase); 
        solve();
    }
    cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
}   
 
int n,k;
int ar[200005];

int cntofproductlessthanx(int x){
    int ans=0;
    loop(i,n)
    {
        if (ar[i]>0)
        {
            int lo=i+1,hi=n-1,mid;
            int idx=i;
            while (lo<=hi){
                mid=(lo+hi)/2;
                int p=ar[i]*ar[mid];
                if (p<x)
                {
                    idx=mid;
                    lo=mid+1;
                }
                else
                    hi=mid-1;
            }
            ans+=idx-i;
        }
        else
        {
            int lo=i+1,hi=n-1,mid;
            int idx=n;
            while (lo<=hi){
                mid=(lo+hi)/2;
                int p=ar[i]*ar[mid];
                if (p<x)
                {
                    idx=mid;
                    hi=mid-1;
                }
                else
                    lo=mid+1;
            }
            ans+=n-idx;
        }
    }
    return ans;
}
void solve(){
    cin>>n>>k;
    loop(i,n)
        cin>>ar[i];
    sort(ar,ar+n);
    int lo=-1e18, hi=1e18,ans;
    while(lo<=hi)
    {
        int mid=(lo+hi)/2;
        if(cntofproductlessthanx(mid)<k)
        {
            ans=mid;
            lo=mid+1;
        }
        else
        {
            hi=mid-1;
        }
    }
    cout<<ans<<endl;
}

Measured memory_bytes: 1792