#include <bits/stdc++.h>
using namespace std;
string func(vector<int> &num){
sort(num.begin(),num.end(),greater<int>());
int diff = num[1] - num[0];
int n = num.size();
for(auto i = 2;i<n;++i){
if(num[i] - num[i-1] != diff)
return "Impossible";
}
return "Possible";
}
int main(){
int n;
while(cin >> n){
vector<int> num(n);
for(auto i = 0;i < n;++i)
cin>>num[i];
cout<<func(num)<<endl;
}
return 0;
}
