import java.io.*;
import java.util.*;

public class MaartenScanner {
    public static void main(String[] args) throws IOException {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            new MaartenScanner().run(new Scanner(reader));
        }
    }

    public void run(Scanner sc) throws IOException {
        int n = sc.nextInt(), r = sc.nextInt();

        // `students` is transposed relative from the input: we have one row per student, instead of one row per topic
        boolean[][] students = new boolean[2 * n][r];
        for (int i = 0; i < r; i++) {
            for (int j = 0; j < 2 * n; j++) {
                students[j][i] = sc.nextInt() > n;
            }
        }

        List<String> studentStrs = new ArrayList<>(2 * n);
        List<String> invertedStrs = new ArrayList<>(2 * n);
        for (int i = 0; i < 2 * n; i++) {
            StringBuilder sb1 = new StringBuilder(r), sb2 = new StringBuilder(r);
            for (int j = 0; j < r; j++) {
                sb1.append(students[i][j] ? "1" : "0");
                sb2.append(students[i][j] ? "0" : "1");
            }
            studentStrs.add(sb1.toString());
            invertedStrs.add(sb2.toString());
        }
        Collections.sort(studentStrs);
        Collections.sort(invertedStrs);

        for (int i = 0; i < 2 * n; i++) {
            if (!studentStrs.get(i).equals(invertedStrs.get(i))) {
                System.out.println("impossible");
                return;
            }
        }
        System.out.println("possible");
    }
}