/*
                ____________    ______________       __
               / _________  /\ /_____   _____/\     / /\
              / /\       / /  \\    /  /\    \ \   / /  \
             / /  \_____/ /   / \__/  /  \____\/  / /   /
            / /   /    / /   /    /  /   /       / /   /
           / /   /    / /   /    /  /   /       / /   /
          / /   /    / /   /    /  /   /       / /   /
         / /___/____/ /   /    /  /   /       / /___/________
        /____________/   /    /__/   /       /______________/\
        \            \  /     \  \  /        \              \ \
         \____________\/       \__\/          \______________\/
           ___       ___               ___    __________
          /  /\     /  /\             /  /\  /_______  /\
         /  /__\___/  /  \           /  /  \ \      /  /  \
        /____    ____/   /          /  /   /  \____/  /   /
        \   /   /\   \  /          /  /   /       /  /   /
         \_/   /  \___\/ ___      /  /   /       /  /   /
          /   /   /     /  /\    /  /   /       /  /   /
         /   /   /     /  /__\__/  /   /       /  /___/____
        /___/   /     /___________/   /       /___________/\
        \   \  /      \           \  /        \           \ \
         \___\/        \___________\/          \___________\/
 
          A FAN OF FIZZYDAVID
 
*/
 
#include<bits/stdc++.h>
 
#define HEAP priority_queue
#define rep(i,n) for(int i=0;i<(n);i++)
#define per(i,n) for(int i=(n)-1;i>=0;i--)
#define forn(i,l,r) for(int i=(l);i<=(r);i++)
#define nrof(i,r,l) for(int i=(r);i>=(l);i--)
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define X first
#define Y second
#define eps 1e-20
#define pi 3.1415926535897932384626433832795
#define orz int
#define yjz main
#define fizzydavid return
#define ak 0
#define la ;
#define SZ(x) (int)x.size()
#define ALL(x) x.begin(),x.end()
#define FILL(a,b) memset((a),(b),sizeof((a)))
 
using namespace std;
 
typedef long long LL;
typedef double flt;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef vector<LL> vl;
typedef pair<int,LL> pil;
typedef pair<LL,int> pli;
typedef pair<LL,LL> pll;
typedef vector<pil> vil;
typedef vector<pii> vii;
 
const int iinf=1e9+7;
const LL linf=1ll<<60;
const flt dinf=1e10;
 
template <typename T>
inline void scf(T &x)
{
	bool f=0; x=0; char c=getchar();
	while((c<'0' || c>'9') && c!='-') c=getchar();
	if(c=='-') { f=1; c=getchar(); }
	while(c>='0' && c<='9') { x=x*10+c-'0'; c=getchar(); }
	if(f) x=-x; return;
}
 
template <typename T1,typename T2>
void scf(T1 &x,T2 &y) { scf(x); return scf(y); }
 
template <typename T1,typename T2,typename T3>
void scf(T1 &x,T2 &y,T3 &z) { scf(x); scf(y); return scf(z); }
 
template <typename T1,typename T2,typename T3,typename T4>
void scf(T1 &x,T2 &y,T3 &z,T4 &w) { scf(x); scf(y); scf(z); return scf(w); }
 
#ifdef ONLINE_JUDGE
#define debug(x) ;
#else
#define DEBUG
#define debug(x) cerr<<#x<<"="<<x<<endl;
#endif
 
//---------------------------head----------------------------
 
const int N=110;
 
int n,mx;
int a[N],cnt[N];
 
orz yjz()
{
    scf(n);
 
    forn(i,1,n)
    {
        scf(a[i]);
        cnt[a[i]]++;
        mx=max(mx,a[i]);
    }
 
    if(n==2)
    {
        if(cnt[1]!=2)
        {
            puts("Impossible");
        }
        else
            puts("Possible");
        fizzydavid ak la
    }
 
    if(n==3)
    {
        if(cnt[2]!=2 || cnt[1]!=1)
        {
            puts("Impossible");
        }
        else
            puts("Possible");
        fizzydavid ak la
    }
 
    if(mx==1)
    {
        puts("Impossible");
        fizzydavid ak la
    }
 
    if(mx==2)
    {
        if(cnt[2]!=n-1 || cnt[1]!=1)
        {
            puts("Impossible");
        }
        else puts("Possible");
        fizzydavid ak la
    }
 
    forn(i,0,mx)
    {
        int d=max(i,mx-i);
        cnt[d]--;
    }
 
    forn(i,0,mx)
    {
        if(cnt[i]<0)
        {
            puts("Impossible");
            fizzydavid ak la
        }
        if(cnt[i] && i+i-2<mx)
        {
            puts("Impossible");
            fizzydavid ak la
        }
    }
 
    puts("Possible");
	fizzydavid ak la
}

Measured memory_bytes: 256