#include<iostream>
#include<cstdio>
#include<cstring>
namespace OoO
{
	const int N=105;
	int c[N];
	int n,L;
	bool check()
	{
		if(L==1 && n>2)return 0;
		if(n==1)return 0;
		if(c[L]==1)return 0;

		c[L]=0;
		int hl=L/2;
		for(int i=L-1;i>hl;i--)
			if(c[i]<2)return 0;
			else c[i]-=2;
		if(L%2==0){if(!c[hl])return 0;c[hl]--;}
		for(int i=1;i<=hl+(L%2);i++)
			if(c[i])return 0;
		return 1;
	}
	void solve()
	{
		scanf("%d",&n);
		for(int i=1,x;i<=n;i++)
			scanf("%d",&x),c[x]++;
		for(int i=n;i;i--)if(c[i]){L=i;break;}
		printf("%s\n",check()?"Possible":"Impossible");
	}
}
int main()
{
	OoO::solve();
	return 0;
}
