#[derive(Default)]
//NOTE
//declare variables to reduce the number of parameters for dp and dfs etc.
struct Solver {}

impl Solver {
    fn solve(&mut self) {
        let stdin = std::io::stdin();
        let mut scn = Scanner {
            stdin: stdin.lock(),
        };
        let n: usize = scn.read();
        let k: usize = scn.read();
        let mut a: Vec<i64> = scn.vec(n);
        a.sort();
        let mut left = -(1i64 << 60);
        let mut right = 1i64 << 60;
        while right - left > 1 {
            let med = (right + left) / 2;

            let mut sum1 = 0usize;
            let mut sum2 = 0usize;
            for &x in a.iter() {
                if x > 0 {
                    let mut l = -1 as isize;
                    let mut r = n as isize;
                    while r - l > 1 {
                        let m = (l + r) / 2;
                        if m < 0 {
                            l = m;
                            continue;
                        } else if m >= n as isize {
                            r = m;
                            continue;
                        }
                        if x * a[m as usize] <= med {
                            l = m;
                        } else {
                            r = m;
                        }
                    }
                    sum1 += r as usize;
                } else if x < 0 {
                    let mut l = -1 as isize;
                    let mut r = n as isize;
                    while r - l > 1 {
                        let m = (l + r) / 2;
                        if m < 0 {
                            l = m;
                            continue;
                        } else if m >= n as isize {
                            r = m;
                            continue;
                        }
                        if x * a[m as usize] <= med {
                            r = m;
                        } else {
                            l = m;
                        }
                    }
                    sum1 += n - r as usize;
                } else {
                    //zero
                    if med >= 0 {
                        sum1 += n;
                    }
                }
                if x * x <= med {
                    sum2 += 1;
                }
            }
            let cnt = (sum1 - sum2) / 2;
            if cnt >= k {
                right = med;
            } else {
                left = med;
            }
        }
        println!("{}", right);
    }
}

fn main() {
    std::thread::Builder::new()
        .stack_size(64 * 1024 * 1024) // 64MB
        .spawn(|| {
            let mut solver = Solver::default();
            solver.solve()
        })
        .unwrap()
        .join()
        .unwrap();
}
pub mod utils {
    const DYX: [(isize, isize); 8] = [
        (0, 1),   //right
        (1, 0),   //down
        (0, -1),  //left
        (-1, 0),  //top
        (1, 1),   //down right
        (-1, 1),  //top right
        (1, -1),  //down left
        (-1, -1), //top left
    ];

    pub fn try_adj(y: usize, x: usize, dir: usize, h: usize, w: usize) -> Option<(usize, usize)> {
        let ny = y as isize + DYX[dir].0;
        let nx = x as isize + DYX[dir].1;
        if ny >= 0 && nx >= 0 {
            let ny = ny as usize;
            let nx = nx as usize;
            if ny < h && nx < w {
                Some((ny, nx))
            } else {
                None
            }
        } else {
            None
        }
    }
}

//snippet from kenkoooo
pub struct Scanner<R> {
    stdin: R,
}

impl<R: std::io::Read> Scanner<R> {
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        use std::io::Read;
        let buf = self
            .stdin
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r')
            .take_while(|&b| b != b' ' && b != b'\n' && b != b'\r')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn read_line(&mut self) -> String {
        use std::io::Read;
        let buf = self
            .stdin
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b'\n' || b == b'\r')
            .take_while(|&b| b != b'\n' && b != b'\r')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }

    pub fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}


Measured memory_bytes: 3228