#include<cstdio>
#include<algorithm>
int a[101],n,vis[101],mx,mn;
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;++i)scanf("%d",a+i);
	std::sort(a+1,a+n+1);
	mx=a[n];
	for(int i=0;i<=mx;++i){
		bool find=0;
		for(int j=1;j<=n;++j)if(!vis[j]&&a[j]==mx-i/2){find=1;vis[j]=1;break;}
		if(!find){puts("Impossible");return 0;}
	}
	for(int i=1;i<=n;++i)if(!vis[i]&&a[i]<=(mx+1)/2){puts("Impossible");return 0;}
	puts("Possible");
	return 0;
}