#include <bits/stdc++.h>
using namespace std;

int main(){
    int n; cin >> n;
    int ans = 0;
    for(int i=0; i<n; i++){
        int tmp; cin >> tmp;
        ans ^= tmp;
    }
    if(ans == 0){
        cout << "possible" << endl;
    }else{
        cout << "impossible" << endl;
    }
}