#include <bits/stdc++.h>
using namespace std;

const int N = 1e2 + 10;

int n, a[N], cnt[N];

inline void go_die() {
	puts("Impossible");
	exit(0);
}

int main() {
	scanf("%d", &n);
	int max_a = INT_MIN, min_a = INT_MAX;
	for (int i = 1; i <= n; ++i) {
		scanf("%d", a + i);
		++cnt[a[i]];
		max_a = max(max_a, a[i]);
		min_a = min(min_a, a[i]);
	}
	if (min_a < (max_a + 1) / 2 || cnt[max_a] < 2) go_die();
	if ((max_a & 1) && cnt[min_a] != 2) go_die();
	if (!(max_a & 1) && cnt[min_a] != 1) go_die();
	for (int i = min_a + 1; i < max_a; ++i)
		if (cnt[i] < 2) go_die();
	puts("Possible");
}