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

int n,mx,mn,cnt[110];

int main()
{
#ifdef h10
	freopen("C.in","r",stdin);
	freopen("C.out","w",stdout);
#endif
	int i,x;
	scanf("%d",&n);
	mx=0; mn=n;
	for (i=1;i<=n;i++)
	{
		scanf("%d",&x);
		cnt[x]++;
		mx=max(mx,x);
		mn=min(mn,x);
	}
	bool flag=1;
	flag&=mn==(mx+1)/2;
	for (i=mn+1;i<=mx;i++)
		flag&=cnt[i]>=2;
	flag&=cnt[mn]==(mx&1)+1;
	puts(flag?"Possible":"Impossible");
}
