use std::collections::*;
use std::io::*;
use std::str::FromStr;
use utils::*;

pub fn main() {
    let i = stdin();
    let mut o = Vec::new();
    run(i.lock(), &mut o);
    stdout().write_all(&o).unwrap();
}

fn run<R: BufRead, W: Write>(i: R, o: &mut W) {
    let mut i = CpReader::new(i);
    let n = i.read::<usize>();
    let w = i.read_vec::<usize>(n);
    let r = if solve(&w) { "possible" } else { "impossible" };
    writeln!(o, "{}", r).unwrap();
}
fn solve(w: &[usize]) -> bool {
    let sum: usize = w.iter().sum();
    if sum % 2 == 1 {
        return false;
    }
    let mut m = BTreeMap::new();
    for &w in w {
        *m.entry(w).or_insert(0) += 1;
    }

    fn get_result<'a>(mut i: btree_map::Iter<'a, usize, usize>, mut l0: usize, l1: usize) -> bool {
        if let Some((&k, &v)) = i.next() {
            for c in 0..v + 1 {
                let l1_use = (v - c) * k;
                if l1_use == l1 || (l1_use < l1 && get_result(i.clone(), l0, l1 - l1_use)) {
                    return true;
                }
                if l0 < k {
                    return false;
                }
                l0 -= k;
                if l0 == 0 {
                    return true;
                }
            }
        }
        false
    }
    get_result(m.iter(), sum / 2, sum / 2)
}

mod utils {
    use super::*;

    pub struct CpReader<R: BufRead> {
        r: R,
        s: String,
    }

    impl<R: BufRead> CpReader<R> {
        pub fn new(r: R) -> Self {
            CpReader {
                r: r,
                s: String::new(),
            }
        }
        pub fn read_line(&mut self) -> &str {
            self.s.clear();
            self.r.read_line(&mut self.s).unwrap();
            self.s.trim()
        }

        pub fn read<T: FromStr>(&mut self) -> T {
            self.read_line().parse().ok().unwrap()
        }

        pub fn read_vec<T: FromStr>(&mut self, n: usize) -> Vec<T> {
            self.read_line()
                .split(' ')
                .take(n)
                .map(|x| x.parse().ok().unwrap())
                .collect()
        }
    }
}