#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1e9 + 7;
const long long MAX = 1e14 + 8;
const long long MAXN = 1e5 + 8;
const long long eps = 1e-4;
long long t[103];
int main() {
  long long n, M = 0;
  cin >> n;
  for (int i = 0; i < n; i++) {
    long long x;
    cin >> x;
    M = max(M, x);
    t[x]++;
  }
  bool b = 1;
  if (t[M] == 1) b = 0;
  if (t[1] > 1) b = 0;
  for (int i = M; i >= ceil(M / 2.0); i--) {
    if (t[i] == 0) b = 0;
  }
  if (!b)
    cout << "Impossible";
  else
    cout << "Possible";
  return 0;
}
