#include <bits/stdc++.h>
using namespace std;
const int N = 105;
int cnt[105];
int main() {
  int a[N], n;
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) scanf("%d", a + i), cnt[a[i]]++;
  int mx = -1;
  for (int i = 1; i <= n; ++i) mx = max(mx, a[i]);
  if ((mx + 1) % 2) {
    int mi = mx / 2 + 1;
    for (int i = mx, cot = 0; cot < mx / 2; ++cot) {
      cnt[i] -= 2;
      if (cnt[i] < 0) return 0 * puts("Impossible");
      i--;
    }
    cnt[mx / 2]--;
    if (cnt[mx / 2] < 0) return 0 * puts("Impossible");
    for (int i = 1; i < n; ++i) {
      if (cnt[i] && i < mi) return 0 * puts("Impossible");
    }
  } else {
    int mi = (mx + 1) / 2 + 1;
    for (int i = mx, cot = 0; cot <= mx / 2; ++cot) {
      cnt[i] -= 2;
      if (cnt[i] < 0) return 0 * puts("Impossible");
      i--;
    }
    for (int i = 1; i < n; ++i) {
      if (cnt[i] && i < mi) return 0 * puts("Impossible");
    }
  }
  puts("Possible");
}
