import java.util.*;

class DisjointSet {
  public int[] upper; // minus:num_element(root) plus:root(normal)
  // public int[] w;

  public DisjointSet(int n) {
    upper = new int[n];
    Arrays.fill(upper, -1);
    // w = new int[n];
  }

  public DisjointSet(DisjointSet ds) {
    this.upper = Arrays.copyOf(ds.upper, ds.upper.length);
  }

  public int root(int x) {
    return upper[x] < 0 ? x : (upper[x] = root(upper[x]));
  }

  public boolean equiv(int x, int y) {
    return root(x) == root(y);
  }

  public boolean union(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (upper[y] < upper[x]) {
        int d = x;
        x = y;
        y = d;
      }
      // w[x] += w[y];
      upper[x] += upper[y];
      upper[y] = x;
    }
    return x == y;
  }

  public int count() {
    int ct = 0;
    for (int u : upper) {
      if (u < 0)
        ct++;
    }
    return ct;
  }

  public int[][] toBucket() {
    int n = upper.length;
    int[][] ret = new int[n][];
    int[] rp = new int[n];
    for (int i = 0; i < n; i++) {
      if (upper[i] < 0)
        ret[i] = new int[-upper[i]];
    }
    for (int i = 0; i < n; i++) {
      int r = root(i);
      ret[r][rp[r]++] = i;
    }
    return ret;
  }
}

@SuppressWarnings("unused")
public class Main {

  private static void solve() {
    int t = ni();
    int r = ni();
    int max = 6000;

    int[][] s = new int[max][3];
    int n = 0;

    int buc = 40;
    int m = 4;
    Set<int[]> list = new HashSet<>();
    for (int i = 0; i < t; i++) {
      for (int v : ask()) {
        s[n][0] = n;
        s[n][1] = v;
        s[n][2] = i;

        list.add(s[n]);
        n++;
      }

      if (list.size() >= buc) {
        int[][] ret = pick(list);
        int[] u = ret[0];
        int[] v = ret[1];
        ans(m - 1, u, v);
      }
    }
  }

  private static int[][] pick(Set<int[]> set) {
    List<int[]> list = new ArrayList<>(set);
    Collections.sort(list, (a, b) -> a[1] - b[1]);
    int min = Integer.MAX_VALUE;
    int minArg = -1;

    int m = 4;
    for (int i = 0; i <= list.size() - m; i++) {
      int a = list.get(i)[1];
      int b = list.get(i + m - 1)[1];

      if (a - b < min) {
        min = a - b;
        minArg = i;
      }
    }
    int[][] ret = new int[m][];
    for (int i = 0; i < m; i++) {
      ret[i] = list.get(minArg + i);
    }

    // remove from list
    for (int i = 0; i < m; i++) {
      set.remove(ret[i]);
    }

    int[] u = new int[m - 1];
    int[] v = new int[m - 1];
    for (int j = 0; j < m - 1; j++) {
      u[j] = ret[j][0];
      v[j] = ret[j + 1][0];
    }
    return new int[][] { u, v };
  }

  private static int[] ask() {
    int n = ni();
    int[] s = na(n);
    return s;
  }

  private static void ans(int m, int[] u, int[] v) {
    out.println(m);
    for (int i = 0; i < m; i++) {
      out.println((u[i] + 1) + " " + (v[i] + 1));
    }
    out.flush();
  }

  public static void main(String[] args) {
    new Thread(null, new Runnable() {
      @Override
      public void run() {
        long start = System.currentTimeMillis();
        String debug = args.length > 0 ? args[0] : null;
        if (debug != null) {
          try {
            is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }
        reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
        solve();
        out.flush();
        tr((System.currentTimeMillis() - start) + "ms");
      }
    }, "", 64000000).start();
  }

  private static java.io.InputStream is = System.in;
  private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
  private static java.util.StringTokenizer tokenizer = null;
  private static java.io.BufferedReader reader;

  public static String next() {
    while (tokenizer == null || !tokenizer.hasMoreTokens()) {
      try {
        tokenizer = new java.util.StringTokenizer(reader.readLine());
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    }
    return tokenizer.nextToken();
  }

  private static double nd() {
    return Double.parseDouble(next());
  }

  private static long nl() {
    return Long.parseLong(next());
  }

  private static int[] na(int n) {
    int[] a = new int[n];
    for (int i = 0; i < n; i++)
      a[i] = ni();
    return a;
  }

  private static char[] ns() {
    return next().toCharArray();
  }

  private static long[] nal(int n) {
    long[] a = new long[n];
    for (int i = 0; i < n; i++)
      a[i] = nl();
    return a;
  }

  private static int[][] ntable(int n, int m) {
    int[][] table = new int[n][m];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[i][j] = ni();
      }
    }
    return table;
  }

  private static int[][] nlist(int n, int m) {
    int[][] table = new int[m][n];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[j][i] = ni();
      }
    }
    return table;
  }

  private static int ni() {
    return Integer.parseInt(next());
  }

  private static void tr(Object... o) {
    if (is != System.in)
      System.out.println(java.util.Arrays.deepToString(o));
  }
}