#include <bits/stdc++.h>
using namespace std;
const int N = 105;
int n, dia, a[N], c[N];
bool cmp(int x, int y) { return x > y; }
int main() {
  cin >> n;
  assert(n < 70);
  for (int i = 1; i <= n; ++i) cin >> a[i];
  sort(a + 1, a + 1 + n, cmp);
  dia = a[1];
  for (int i = 1; i <= n; ++i) ++c[a[i]];
  if (dia == 1 && n != 2) return puts("Impossible"), 0;
  int t = (a[1] + 1) >> 1;
  for (int i = 1; i < t; ++i)
    if (c[i]) return puts("Impossible"), 0;
  if ((~a[1] & 1) && c[t] != 1) return puts("Impossible"), 0;
  if (~a[1] & 1) ++t;
  for (int i = t; i <= a[1]; ++i)
    if (c[i] < 2) return puts("Impossible"), 0;
  puts("Possible");
  return 0;
}
