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 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 set) { List 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)); } }