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

const int MAXN = 110;
int n, a[MAXN], c[MAXN], r;

int main() {
	cin >> n;
	for(int i = 1; i <= n; i++) {
		cin >> a[i];
		c[a[i]]++;
		r = max(r, a[i]);
	}
	int i;
	for(i = r; i > ((r+1)>>1); i--) {
		if(c[i] < 2) {
			printf("Impossible\n");
			return 0;
		}
		c[i] -= 2;
	}
	if(r & 1) {
		if(c[i] < 2) {
			printf("Impossible\n");
			return 0;
		}
		c[i] -= 2;
	}
	else {
		if(c[i] < 1) {
			printf("Impossible\n");
			return 0;
		}
		c[i]--;
	}
	for(i = ((r+1)>>1); i >= 0; i--) {
		if(c[i]) {
			printf("Impossible\n");
			return 0;
		}
	}

	printf("Possible\n");
	return 0;
}
