macro_rules ! input { ( source = $ s : expr , $ ( $ r : tt ) * ) => { let mut iter = $ s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; ( $ ( $ r : tt ) * ) => { let s = { use std :: io :: Read ; let mut s = String :: new ( ) ; std :: io :: stdin ( ) . read_to_string ( & mut s ) . unwrap ( ) ; s } ; let mut iter = s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; }
macro_rules ! input_inner { ( $ iter : expr ) => { } ; ( $ iter : expr , ) => { } ; ( $ iter : expr , mut $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let mut $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , mut $ var : ident $ ( $ r : tt ) * ) => { let mut $ var = $ iter . next ( ) . unwrap ( ) . parse ::< usize > ( ) . unwrap ( ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident $ ( $ r : tt ) * ) => { let $ var = $ iter . next ( ) . unwrap ( ) . parse ::< usize > ( ) . unwrap ( ) ; input_inner ! { $ iter $ ( $ r ) * } } ; }
macro_rules ! read_value { ( $ iter : expr , ( $ ( $ t : tt ) ,* ) ) => { ( $ ( read_value ! ( $ iter , $ t ) ) ,* ) } ; ( $ iter : expr , [ $ t : tt ; $ len : expr ] ) => { ( 0 ..$ len ) . map ( | _ | read_value ! ( $ iter , $ t ) ) . collect ::< Vec < _ >> ( ) } ; ( $ iter : expr , chars ) => { read_value ! ( $ iter , String ) . chars ( ) . collect ::< Vec < char >> ( ) } ; ( $ iter : expr , usize1 ) => { read_value ! ( $ iter , usize ) - 1 } ; ( $ iter : expr , $ t : ty ) => { $ iter . next ( ) . unwrap ( ) . parse ::<$ t > ( ) . unwrap ( ) } ; }
trait Bisect: Copy {
    fn halve(self, other: Self) -> Self;
    fn section_end(self, other: Self) -> bool;
}
impl Bisect for usize {
    fn halve(self, other: Self) -> Self {
        if self > other {
            other + (self - other) / 2
        } else {
            self + (other - self) / 2
        }
    }
    fn section_end(self, other: Self) -> bool {
        (if self > other {
            self - other
        } else {
            other - self
        }) <= 1
    }
}
impl Bisect for i64 {
    fn halve(self, other: Self) -> Self {
        (self + other) / 2
    }
    fn section_end(self, other: Self) -> bool {
        (self - other).abs() <= 1
    }
}
fn binary_search<T: Bisect, F: Fn(T) -> bool>(f: F, ok: T, err: T) -> T {
    let mut ok = ok;
    let mut err = err;
    while !ok.section_end(err) {
        let m = ok.halve(err);
        if f(m) {
            ok = m;
        } else {
            err = m;
        }
    }
    ok
}
const INF: i64 = 1_000_000_000_000_000_001;
const MINF: i64 = -1_000_000_000_000_000_001;
fn main() {
    input! { n, k, mut a: [i64; n] };
    a.sort();
    let f = |x| {
        let mut res = 0;
        for i in 0..n - 1 {
            let b = a[i];
            if b < 0 {
                res += n - binary_search(|j| b * a[j] < x, n, i);
            } else {
                res += binary_search(|j| b * a[j] < x, i, n) - i;
            }
        }
        res < k
    };
    println!("{}", binary_search(f, MINF, INF));
}


Measured memory_bytes: 8444