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

const int N = 100;
int a[N], cnt[N], n;

int main() {
    cin >> n;
    for (int i = 0; i < n; ++i) cin >> a[i], ++cnt[a[i]];
    int len = *max_element(a, a + n);
    for (int i = 0; i <= len; ++i) {
        if (cnt[max(i, len - i)]-- == 0) {
            cout << "Impossible" << endl;
            return 0;
        }
    }
    for (int i = 1; i <= (len + 1) / 2; ++i) if (cnt[i] > 0) {
        cout << "Impossible" << endl;
        return 0;
    }
    cout << "Possible" << endl;
    return 0;
}
