#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>

using namespace std;

const int N=109;

int n,mv=2e9;
int a[N],tot;
int cnt[N];

inline void end()
{
	puts("Impossible");
	exit(0);
}

int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		if(a[i]>n)end();
		cnt[a[i]]++;
		mv=min(mv,a[i]);
	}	
	
	tot=n;
	if(cnt[mv]>2)end();
	tot-=cnt[mv];
	for(int i=mv+1;i<=mv*2-(!(cnt[mv]&1));i++)
	{
		if((cnt[i]<=1 && tot>0))end();
		tot-=cnt[i];
	}
	if(tot==0)
		puts("Possible");
	else
		end();
	return 0;
}
