#include <bits/stdc++.h>
using namespace std;
long long read() {
  long long x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = (x << 3) + (x << 1) + ch - '0';
    ch = getchar();
  }
  return x * f;
}
int n, m;
int a[200005];
int l[200005], r[200005];
int main() {
  int i, j, group, x, y, v, Case = 0;
  n = read();
  for (i = 1; i <= n; ++i) a[i] = read();
  sort(a + 1, a + n + 1);
  if (a[n] >= n) return 0 * printf("Impossible\n");
  if (n == 2 && a[n] != 1) return 0 * printf("Impossible\n");
  if (n > 2 && a[2] == 1) return 0 * printf("Impossible\n");
  int temp = n - a[n];
  for (i = n - 1; temp; --temp, --i) {
    if (a[i] != a[n]) return 0 * printf("Impossible\n");
  }
  int k = 2;
  for (; i; --i) {
    if (a[i] != a[n] - k / 2) return 0 * printf("Impossible\n");
    ++k;
  }
  printf("Possible\n");
  return 0;
}
