#include <bits/stdc++.h>
using namespace std;
int q[200], q1[200];
int main() {
  int a;
  scanf("%d", &a);
  for (int i = 0; i < a; i++) {
    scanf("%d", &q[i]);
    q1[q[i]]++;
  }
  int maxx = -1;
  for (int i = 0; i < a; i++) {
    maxx = max(maxx, q[i]);
  }
  int flag = 0;
  if (maxx & 1) {
    int q2 = (maxx - 1) / 2;
    for (int i = 0; i < q2; i++) {
      if (q1[maxx - i] < 2) flag = 1;
    }
    if (q1[maxx - q2] != 2) flag = 1;
  } else {
    int q2 = (maxx) / 2;
    for (int i = 0; i < q2; i++) {
      if (q1[maxx - i] < 2) flag = 1;
    }
    if (q1[maxx - q2] != 1) flag = 1;
  }
  if (flag)
    printf("Impossible\n");
  else
    printf("Possible\n");
}
