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

#define for_(i,a,b) for(int i=(a);i<(b);++i)

void isyes() { puts("Possible"); exit(0); }
void isno() { puts("Impossible"); exit(0); }

int N, a[111];

void solve () {
	vector< int > cnt(N, 0);
	for_(i,0,N) cnt[a[i]]++;
	
	int max_a = *max_element(a, a + N);
	if (cnt[max_a] < 2) isno();	
	if (max_a == 1 && N > 2) isno();
		
	if (max_a % 2 == 0 && cnt[max_a / 2] != 1) isno();
	if (max_a % 2 && cnt[max_a / 2] > 0) isno();
	if (max_a % 2 && cnt[max_a / 2 + 1] > 2) isno();
	for_(x,max_a/2+1,max_a) if (cnt[x] < 2) isno();
	
	isyes();
}

int main() {
	cin >> N;
	for_(i,0,N) cin >> a[i];
	solve();
}