/**
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
*/
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <queue>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cassert>

#define F first
#define S second
#define endl '\n'
#define deb(x) cout<<#x<<' '<<x<<endl;
#define pb push_back

/*
#ifdef IZI_KATKA
#define int __int64_t
#else
#define int __int64
#endif
*/

const long long MOD = 1e9 + 7;
const long long MAXN = 1e6 + 1;
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;


long long readInt() {
    bool minus1 = false;
    long long result = 0;
    char ch;
    ch = getchar();
    while (true) {
        if (ch == '-') break;
        if (ch >= '0' && ch <= '9') break;
        ch = getchar();
    }
    if (ch == '-') minus1 = true; else result = ch-'0';
    while (true) {
        ch = getchar();
        if (ch < '0' || ch > '9') break;
        result = result*10 + (ch - '0');
    }
    if (minus1)
        return -result;
    else
        return result;
}


int main() {
	#ifdef IZI_KATKA
	assert(freopen("input", "r", stdin));
    assert(freopen("output", "w", stdout));
    #endif
    int n = readInt();
    int mx = 0;
	multiset<int> s;
    for (int i = 1; i <= n; i++) {
    	int x = readInt();
    	s.insert(x);
    	mx = max(mx, x);
    }
	if (mx % 2 == 0) {
		for (int i = mx; i >= mx / 2; i--) {
			if (s.find(i) == s.end()) {
				cout << "Impossible";
				return 0;
			}
			s.erase(s.find(i));
			if (i == mx / 2) continue;
			if (s.find(i) == s.end()) {
				cout << "Impossible";
				return 0;
			}
			s.erase(s.find(i));	
		}
		if (s.size() >= 1) {
			if (!((mx) / 2 + 1 <= *s.begin() && *s.begin() <= mx)) {
				cout << "Impossible";
				return 0;				
			}
		}
		if (s.size() >= 2) {
			auto Z = s.end();
			Z--;
			int K = *Z;			
			if (!((mx) / 2 + 1 <= K && K <= mx)) {
				cout << "Impossible";
				return 0;				
			}
		} 
		cout << "Possible";
	} else {
		for (int i = mx; i >= (mx+1) / 2; i--) {
			if (s.find(i) == s.end()) {
				cout << "Impossible";
				return 0;
			}
			s.erase(s.find(i));
			if (s.find(i) == s.end()) {
				cout << "Impossible";
				return 0;
			}
			s.erase(s.find(i));	
		}
		if (s.size() >= 1) {
			if (!((mx + 1) / 2 + 1 <= *s.begin() && *s.begin() <= mx)) {
				cout << "Impossible";
				return 0;				
			}
		}
		if (s.size() >= 2) {
			auto Z = s.end();
			Z--;
			int K = *Z;			
			if (!((mx + 1) / 2 + 1 <= K && K <= mx)) {
				cout << "Impossible";
				return 0;				
			}
		}
		cout << "Possible";
		return 0;     
	}       
    return 0;
}

Measured memory_bytes: 256