#include<cstdio>
#include<algorithm>
using namespace std;
const int N=110;
int i,j,k,n,m,ma,mi;
int a[N],nm[N];
int main() {
	scanf("%d",&n);
	mi=n;
	for (i=1;i<=n;i++) {
		scanf("%d",&a[i]);
		nm[a[i]]++;
		ma=max(ma,a[i]);
		mi=min(mi,a[i]);
	}
	k=(ma+1)/2;
	if (mi<k) return puts("Impossible"),0;
	if (ma&1) {
		if (nm[k]!=2) return puts("Impossible"),0;
	}
	else {
		if (nm[k]!=1) return puts("Impossible"),0;
	}
	for (i=k+1;i<=ma;i++) if (nm[i]<2) return puts("Impossible"),0;
	puts("Possible");
}