#![allow(non_snake_case, unused_must_use, unused_imports)]
use std::io::{self, prelude::*};

fn main() {
    let (stdin, stdout) = (io::read_to_string(io::stdin()).unwrap(), io::stdout());
    let (mut stdin, mut buffer) = (stdin.split_whitespace(), io::BufWriter::new(stdout.lock()));

    macro_rules! input {
        ($t: tt, $n: expr) => {
            (0..$n).map(|_| input!($t)).collect::<Vec<_>>()
        };
        (Chars) => {
            input!(String).chars().collect::<Vec<_>>()
        };
        (Usize1) => {
            stdin.next().unwrap().parse::<usize>().unwrap() - 1
        };
        ($t: ty) => {
            stdin.next().unwrap().parse::<$t>().unwrap()
        };
    }

    let N = input!(usize);
    let W = input!(u32, N);

    let mut hq = std::collections::BinaryHeap::from_iter(W.into_iter());

    while hq.len() >= 2 {
        let a = hq.pop().unwrap();
        let b = hq.pop().unwrap();

        hq.push(a - b);
    }

    if hq.pop().unwrap() == 0 {
        writeln!(buffer, "possible");
    } else {
        writeln!(buffer, "impossible");
    }

}