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