#include<bits/stdc++.h>

using namespace std;


int N, A[201], B[200];

void F()
{
  cout << "Impossible" << endl;
  exit(0);
}

int main()
{
  cin >> N;

  int low = 0;
  for(int i = 0; i < N; ++i) {
    int K;
    cin >> K;
    B[i] = K;
    A[K]++;
    low = max(low, K);
  }

  int cost = low + 1;
  int small = N;
  for(int i = 0; i <= low; i++) {
    if(i <= low / 2) cost--;
    if(i > (low + 1) / 2) ++cost;
    --A[cost];

    if(A[cost] < 0) F();
    small = min(small, cost);
  }

  for(int i = 0; i < small; i++) {
    if(A[i] > 0) F();
  }
  if(A[small] >= 1) F();

  cout << "Possible" << endl;
}
