#include "pch.h"

#include <string>

#include<iostream>

#include<map>

#include<memory.h>

#include<vector>

#include<algorithm>

#include<queue>

#include<vector>

#include<stack>

#include<math.h>

#include<iomanip>

#include<bitset>

namespace cc

{

    using std::cout;

    using std::endl;

    using std::cin;

    using std::map;

    using std::vector;

    using std::string;

    using std::sort;

    using std::priority_queue;

    using std::greater;

    using std::vector;

    using std::swap;

    using std::stack;

    using std::bitset;

    constexpr int N = ;

    int a[N];

    int n;

    bool check()

    {

        for (int i = ;i < n - ;i++)

        {

            sort(a + i, a + n, greater<int>());

            if (i + a[i] >= n) return false;

            for (int j = i + ;j <= i + a[i];++j)

            {

                --a[j];

                if (a[j] < )return false;

            }

        }

        if (a[n - ] != )

            return false;

        return true;

    }

    void solve()

    {

        while (cin >> n && n)

        {

            memset(a, , sizeof(a));

            int ok = ;

            for (int i = ;i < n;i++)

            {

                cin >> a[i];

                if (a[i] >= n)

                {

                    ok = ;

                }

            }

            if (ok ==  && check())

            {

                cout << "Possible" << endl;

            }

            else

            {

                cout << "Not possible" << endl;

            }

        }

    }

};

int main()

{

#ifndef ONLINE_JUDGE

    freopen("d://1.text", "r", stdin);

#endif // !ONLINE_JUDGE

    cc::solve();

    return ;

}