#[allow(dead_code)]
fn is_whitespace(c: &char) -> bool {
    c.is_whitespace()
}

#[allow(dead_code)]
fn is_eol(c: &char) -> bool {
    ['\r', '\n'].contains(c)
}

#[allow(unused_macros)]
macro_rules! input {
    ($var:ident, $($r:tt)*) => {
        input_inner!{$var, $($r)*}
    };

    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        #[allow(unused_mut, unused_variables, bare_trait_objects)]
        let mut next = move |f: &Fn(&char)->bool| -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|f(&c))
                .take_while(|c|!f(&c))
                .collect()
        };
        input_inner!{next, $($r)*};
    };
}

#[allow(unused_macros)]
macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };

    ($next:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; eol ]) => {
        $next(&is_eol).split(' ').map(|x| x.parse::<$t>().unwrap()).collect::<Vec<_>>()
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, parser) => {
        $next
    };

    ($next:expr, $t:ty) => {
        $next(&is_whitespace).parse::<$t>().expect("Parse error")
    };
}

#[allow(unused_imports)]
use std::cmp::{max, min};
#[allow(unused_imports)]
use std::collections::{BinaryHeap, HashMap, HashSet};

#[allow(dead_code)]
struct Edge {
    from: usize,
    to: usize,
}

#[allow(dead_code)]
type Graph = Vec<Vec<usize>>;
#[allow(dead_code)]
const M: usize = 1_000_000_007;

fn main() {
    input! {
        n: usize,
        k: usize,
        a: [isize; n],
    }

    let mut pos = vec![];
    let mut neg = vec![];
    let mut zeros = 0isize;

    for x in a {
        if x > 0 {
            pos.push(x);
        } else if x < 0 {
            neg.push(x);
        } else {
            zeros += 1;
        }
    }

    let mut ng = -1e18 as isize;
    let mut ok = 1e18 as isize;
    pos.sort();
    neg.sort();
    neg.reverse();

    while (ok - ng).abs() > 1 {
        let mid = (ok + ng) / 2;
        let mut cnt = 0;

        if mid > 0 {
            cnt += (zeros * (zeros - 1) / 2
                + zeros * pos.len() as isize
                + zeros * neg.len() as isize) as usize;
            cnt += pos.len() * neg.len();

            if !pos.is_empty() {
                let mut r = pos.len() - 1;
                for l in 0..pos.len() {
                    while pos[l] * pos[r] > mid {
                        if r == 0 {
                            break;
                        }
                        r -= 1;
                    }
                    if l >= r {
                        break;
                    }
                    if pos[l] * pos[r] <= mid {
                        cnt += r - l;
                    }
                }
            }

            if !neg.is_empty() {
                let mut r = neg.len() - 1;
                for l in 0..neg.len() {
                    while neg[l] * neg[r] > mid {
                        if r == 0 {
                            break;
                        }
                        r -= 1;
                    }
                    if l >= r {
                        break;
                    }
                    if neg[l] * neg[r] <= mid {
                        cnt += r - l;
                    }
                }
            }
        } else if mid < 0 {
            if !neg.is_empty() {
                let mut n = neg.len() - 1;
                for p in 0..pos.len() {
                    while n > 0 && pos[p] * neg[n - 1] <= mid {
                        n -= 1;
                    }
                    if pos[p] * neg[n] <= mid {
                        cnt += neg.len() - n;
                    }
                }
            }
        } else {
            cnt += (zeros * (zeros - 1) / 2
                + zeros * pos.len() as isize
                + zeros * neg.len() as isize) as usize;
            cnt += pos.len() * neg.len();
        }
        if cnt >= k {
            ok = mid;
        } else {
            ng = mid;
        }
    }

    println!("{}", ok)
}


Measured memory_bytes: 10492