#include <bits/stdc++.h>

#define pb push_back
#define left lleft
#define right rright
#define lld long long

using namespace std;

int N;
int a[102],cnt[102];

void impossible(){
	puts("Impossible");
	exit(0);
}

int main(){
	scanf("%d",&N);
	int big = 0;
	for(int i=1; i<=N; i++){
		scanf("%d",&a[i]);
		cnt[a[i]]++;
		big = max(big,a[i]);
	}
	if(cnt[big] < 2) impossible();
	for(int i=0; i<=big; i++){
		if(cnt[max(i,big-i)] == 0) impossible();
		cnt[max(i,big-i)]--;
	}
	for(int i=1; i<N; i++){
		if(cnt[i] == 0) continue;
		if(i < max(big/2,big-big/2)+1) impossible();
	}
	puts("Possible");

	return 0;
}