ncpc_b

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

public class E {
    FastScanner in;
    PrintWriter out;

    int k, n;
    final String possible = "possible";
    final String impossible = "impossible";
    long[][] neigh;
    long START;
    int it = 0;

    void go(long used1, long used2, int alr) {
        if (alr >= k) {
            out.println(possible);
            out.close();
            System.exit(0);
        }
        if (alr + n - Long.bitCount(used1) - Long.bitCount(used2) < k)
            return;
        it++;
        if (it % 10000 == 0) {
            if (System.currentTimeMillis() - START > 900) {
                out.println(impossible);
                out.close();
                System.exit(0);
            }
        }
        for (int i = 0; i < n; i++) {
            long n1 = neigh[0][i], n2 = neigh[1][i];
            long nused1 = used1, nused2 = used2;
            if (i < 64) {
                if (((1L << i) & used1) != 0)
                    continue;
                nused1 ^= 1L << i;
            } else {
                if (((1L << (i & 63)) & used2) != 0)
                    continue;
                nused2 ^= 1L << (i & 63);
            }
            n1 &= ~used1;
            n2 &= ~used2;
            go(nused1 ^ n1, nused2 ^ n2, alr + 1);
            if (Long.bitCount(n1) + Long.bitCount(n2) >= 2) {
                go(nused1, nused2, alr);
            }
            break;
        }
    }

    void solve() {
        k = in.nextInt();
        n = in.nextInt();
        START = System.currentTimeMillis();
        if (n >= k * 5) {
            out.println(possible);
            return;
        }
        neigh = new long[2][n];
        Random rnd = new Random(123);
        int[] perm = new int[n];
        for (int i = 0; i < n; i++) {
            int pos = rnd.nextInt(i + 1);
            perm[i] = perm[pos];
            perm[pos] = i;
        }
        for (int ii = 0; ii < n; ii++) {
            int i = perm[ii];
            int t = in.nextInt();
            for (int j = 0; j < t; j++) {
                int next = perm[in.nextInt() - 1];
                if (next < 64) {
                    neigh[0][i] ^= 1L << next;
                } else {
                    neigh[1][i] ^= 1L << (next & 63);
                }
            }
        }
        go(0, 0, 0);
        out.println(impossible);
    }

    void run() {
        try {
            in = new FastScanner(new File("E.in"));
            out = new PrintWriter(new File("E.out"));

            solve();

            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    void runIO() {

        in = new FastScanner(System.in);
        out = new PrintWriter(System.out);

        solve();

        out.close();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner(File f) {
            try {
                br = new BufferedReader(new FileReader(f));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        public FastScanner(InputStream f) {
            br = new BufferedReader(new InputStreamReader(f));
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return null;
                st = new StringTokenizer(s);
            }
            return st.nextToken();
        }

        boolean hasMoreTokens() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return false;
                st = new StringTokenizer(s);
            }
            return true;
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }
    }

    public static void main(String[] args) {
        new E().runIO();
    }
}