import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
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 enumerate_all_pairs {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		Map<List<Long>, Integer> map = new HashMap<List<Long>, Integer>();
		Map<List<Long>, Integer> sum = new HashMap<List<Long>, Integer>();
		
		int n = sc.nextInt();
		for(int i = 0; i < n; i++)
		{
			List<Long> tuple = new ArrayList<Long>();
			tuple.add(sc.nextLong());
			tuple.add(sc.nextLong());
			int count = map.containsKey(tuple) ? map.get(tuple) : 0;
			map.put(tuple, count + 1);
		}
		
		for (Entry<List<Long>, Integer> entry1 : map.entrySet())
		{
			List<Long> tuple1 = entry1.getKey();
						
			for (Entry<List<Long>, Integer> entry2 : map.entrySet())
			{
				List<Long> tuple2 = entry2.getKey();
				
				List<Long> sum_tuple = new ArrayList<Long>();
				sum_tuple.add(tuple1.get(0) + tuple2.get(0));
				sum_tuple.add(tuple1.get(1) + tuple2.get(1));
				
				int count = sum.containsKey(sum_tuple) ? sum.get(sum_tuple) : 0;
				
				if(tuple1 == tuple2)
				{
					if(entry1.getValue() % 2 == 0)
						sum.put(sum_tuple, count + entry1.getValue());
				}
				else 
				{
					if(entry1.getValue() == entry2.getValue())
						sum.put(sum_tuple, count + entry1.getValue());
				}					
			}			
		}
		
		
		for (Entry<List<Long>, Integer> entry : sum.entrySet())
			if(entry.getValue() == n)
			{
				System.out.print("possible");
				return;
			}
		
		System.out.print("impossible");

	}

}