#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using VI = vector<int>;
using VL = vector<ll>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define allpt(v) (v).begin(), (v).end()
#define allpt_c(v) (v).cbegin(), (v).cend()
#define allpt_r(v) (v).rbegin(), (v).rend()

const int mod = 1e9 + 7;
const string wsp = " ";
const string tb = "\t";
const string rt = "\n";

template <typename T>
void show1dvec(const vector<T> &v)
{
    if (v.size() == 0)
        return;
    int n = v.size() - 1;
    rep(i, n) cout << v[i] << wsp;
    cout << v[n] << rt;
    return;
}

template <typename T>
void show2dvec(const vector<vector<T>> &v)
{
    int n = v.size();
    rep(i, n) show1dvec(v[i]);
}

template <typename T, typename S>
void show1dpair(const vector<pair<T, S>> &v)
{
    int n = v.size();
    rep(i, n) cout << v[i].first << wsp << v[i].second << rt;
    return;
}

template <typename T, typename S>
void pairzip(const vector<pair<T, S>> &v, vector<T> &t, vector<T> &s)
{
    int n = v.size();
    rep(i, n)
    {
        t.push_back(v[i].first);
        s.push_back(v[i].second);
    }
    return;
}

template <typename T>
void maxvec(vector<T> &v)
{
    T s = v[0];
    int n = v.size();
    rep(i, n - 1)
    {
        if (s > v[i + 1])
        {
            v[i + 1] = s;
        }
        s = v[i + 1];
    }
}

template <typename T, typename S>
bool myfind(T t, S s)
{
    return find(t.cbegin(), t.cend(), s) != t.cend();
}

vector<int> make_kmp_table(string t)
{
    int lt = t.length();
    VI kmptable(lt, 0);
    kmptable[0] = -1;

    return kmptable;
}

int main()
{

#ifdef DEBUG
    cout << "DEBUG MODE" << endl;
    ifstream in("input.txt"); //for debug
    cin.rdbuf(in.rdbuf());    //for debug
#endif

    // int n;
    // string s, t;
    // cin >> n >> s;
    // VL dp(n + 1, 0ll);
    // vector<set<int>> callspell(n);
    // dp[0] = 1;
    // rep(i, n)
    // {
    //     cin >> t;
    // }

    // rep(i, n)
    // {
    //     for (int z : callspell[i])
    //     {
    //         dp[i + z - 1] += dp[i - 1];
    //         dp[i + z - 1] %= mod;
    //     }
    // }

    // cout << dp[n] << rt;

    int n, x, y, mina, maxa;
    cin >> n;
    VI v(n + 1), a(n);
    bool judge = true;
    string ans = "Impossible";
    rep(i, n)
    {
        cin >> a[i];
        v[a[i]]++;
    }
    mina = *min_element(allpt_c(a)), maxa = *max_element(allpt_c(a));
    if (maxa == 2 * mina)
    {
        rep2(i, mina, maxa + 1)
        {
            if (i == mina && v[mina] != 1)
                judge = false;
            else if (i > mina && v[i] < 2)
                judge = false;
        }
        if (judge) ans = "Possible";
    }

    
    else if (maxa == 2 * mina - 1)
    {
        rep2(i, mina, maxa + 1)
        {
            if (i == mina && v[mina] != 2)
                judge = false;
            else if (i > mina && v[i] < 2)
                judge = false;
        }
        if (judge) ans = "Possible";
    }

    cout << ans << rt;



}


Measured memory_bytes: 256