#include<iostream>
#include<vector>
#include<set>
using namespace std;

int main(){
    int n;
    set<int> check;
    check.insert(0);

    cin >> n;
    for(int i=0;i<n;i++){
        int buf;
        cin >> buf;

        set<int> memo;
        auto it = check.begin();
        while(it != check.end()){
            memo.insert( *it + buf );
            memo.insert( *it - buf );
            it++;
        }

        check = memo;
    }
    cout << (check.count(0) == 1 ? "possible" : "impossible") << endl;
}