#include<stdio.h>
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define f(i,x,n) for (int i = x;i < n;++i)

int x[101], y[101];

void no() {
	printf("Impossible\n");
	exit(0);
}

int main() {
	int n;
	scanf("%d", &n);
	int mx = 0, mn = 1e9;
	f(i, 0, n) {
		int t;
		scanf("%d", &t);
		++x[t];
		if (t > mx)mx = t;
		if (t < mn)mn = t;
	}
	if (x[mx] == 1)no();
	if (n > 2 && mx == 1)no();
	int z = mx - mx / 2;
	if (mn != z)no();
	if (mx & 1 && x[mn] != 2)no();
	if (!(mx & 1) && x[mn] != 1)no();
	int r = mx;
	while (r > mn) {
		if (x[r] < 2)no();
		--r;
	}
	printf("Possible\n");
}