#include<bits/stdc++.h>
#define N (1001)
using namespace std;
int n,a[N],Keg[N],maxn;
int main()
{
	scanf("%d",&n);
	for (int i=1; i<=n; ++i)
	{
		scanf("%d",&a[i]);
		Keg[a[i]]++; maxn=max(maxn,a[i]);
	}
	for (int i=(maxn+1)/2; i<=maxn; ++i)
	{
		if (maxn%2==0 && i==(maxn+1)/2) Keg[i]-=1;
		else Keg[i]-=2;
		if (Keg[i]<0){puts("Impossible"); return 0;}
	}
	for (int i=1; i<=(maxn+1)/2; ++i)
		if (Keg[i]) {puts("Impossible"); return 0;}
	puts("Possible");
}