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

#define int long long
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define REP(i, n) for (int i = 0; i < n; ++i)
#define range(i,a,b) ((a)<=(i) && (i)<(b))
#define debug(x) cout << #x << " = " << (x) << endl;
#define fs first
#define sc second
#define pb push_back
#define eb emplace_back
#define SP << " " <<

typedef long long ll;
typedef pair<int, int> P;
typedef tuple<int, int, int> T;
typedef vector<int> vec;
typedef vector<P> pvec;
typedef vector<vector<int>> vvec;
typedef vector<vector<P>> pvvec;
typedef priority_queue<int> PQI;
typedef priority_queue<P> PQP;
typedef priority_queue<int,vector<int>,greater<int>> PQIG;
typedef priority_queue<P,vector<P>,greater<P>> PQPG;

const vector<int> DX = {0, -1, 0, 1, 1, 1, -1, -1};
const vector<int> DY = {1, 0, -1, 0, 1, -1, 1, -1};
constexpr int MOD = (1000000007);
// const int MOD = (998244353);
// const int INF = (1 << 30); // 1073741824
const ll INF = (1LL << 60); // 1152921504606846976
const double PI = (3.141592653589794);
const double EPS = (0.0000000001); // 10^(-10)

template<class T> inline bool chmin(T& a, T b) {if (a > b) {a = b; return 1;} return 0;}
template<class T> inline bool chmax(T& a, T b) {if (a < b) {a = b; return 1;} return 0;}
template<class T> inline T ceil(T a, T b) {return T((a + b - 1) / b);}
template<class T> inline T round(T a, T b) {return T(a / b);}
template< typename T1, typename T2 > istream &operator>>(istream &is, pair< T1, T2 > &p) { is >> p.first >> p.second; return is; }
template <class T> inline void out(T &a) { bool flag=true; for(auto&x:a){if(flag) {flag=false;} else{ cout << ' '; } cout<<x; } cout << endl; }



//----------------------------------------------------------------
int nmax=200000; // 2*(10^5)
vvec G(nmax);





void solve4ts()
{
    
    int n;
    cin>>n;
    vector<int> a(n);
    rep(i,n) cin >> a[i];
    map<int,int> mp;
    rep(i,n){
        mp[a[i]]++;
    }      
    int ng=0;
    int sai=-1;
    int memo=0;
    int saisai=0;
    for(auto x:mp){
        // cout<<x.fs<<" "<<x.sc<<endl;
        if(sai==-1){
            sai=x.sc;
            memo=x.fs;
            saisai=x.fs;
        }
        else{
            if(memo+1==x.fs&&x.sc>=2){

            }
            else{
                ng++;
            }

            memo=x.fs;
        }
    }
    if(n==2&&mp[1]==2){
        cout<<"Possible"<<endl;
        return;
    }
    else if(mp[1]>=2){
        cout<<"Impossible"<<endl;
        return;
    }
    else if(n==2){
        cout<<"Impossible"<<endl;
        return;
    }
    if(sai==1||sai==2){
        if(sai==2){
            if(n%2==1){
                if(saisai==(memo)/2){
                    ng++;
                }
            }
        }
    }
    else{
        ng++;
    }

    if(memo%2==0){
        memo/=2;
    }
    else{
        memo=memo/2+1;
    }

    if(memo!=saisai) {cout<<"Impossible"<<endl;return;}

    if(ng==0) cout<<"Possible"<<endl;
    else cout<<"Impossible"<<endl;
}
//-----------------------------------------------------------------

signed main(){ ios::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(15);
    int repeat = 1;
    // cin >> repeat;
    while(repeat--) solve4ts();
}

Measured memory_bytes: 4992