import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;

// This code fails to work as different instances of the same long list are not seen as the same element.

public class array_instead_of_List {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		Map<long[], Integer> map = new HashMap<long[], Integer>();
		long[] avg = {0,0};
		
		int n = sc.nextInt();
		for(int i = 0; i < n; i++)
		{
			long[] tuple = {sc.nextLong(), sc.nextLong()};
			avg[0] += tuple[0];
			avg[1] += tuple[1];
			int count = map.containsKey(tuple) ? map.get(tuple) : 0;
			map.put(tuple, count + 1);
		}
		if(((2 * avg[0]) % n == 0) && ((2 * avg[1]) % n == 0))
		{
			long[] goal = {2 * avg[0] / n, 2 * avg[1] / n};
			Boolean possible = true;
			for (Entry<long[], Integer> entry : map.entrySet())
			{
				long[] tuple = entry.getKey();
				long[] teammate = {goal[0] - tuple[0], goal[1] - tuple[1]};
				if(tuple == teammate)
				{
					if(entry.getValue() % 2 != 0)
						possible = false;
						break;
				}
				else if(!map.containsKey(teammate) || map.get(teammate) != entry.getValue())
				{
					possible = false;
					break;
				}
			}
			if(possible)
			{
				System.out.print("possible");
				return;
			}
		}
		
		System.out.print("impossible");

	}

}