import java.util.*;
public class Main{
    public static void main(String arg[]){
        Scanner sc = new Scanner(System.in);
        int T = sc.nextInt();
        int R = sc.nextInt();
        int N = 5400;
        Node[] list = new Node[N];
        int user = 1;
        for(int i = 0; i < T; i++){
            int G = sc.nextInt();
            while(G > 0){
                int v = sc.nextInt();
                list[user - 1] = new Node(user, v);
                G--;
                user++;
            }
            if(i < T - 1){
            	System.out.println("0");
            	System.out.flush();
            }
        }
        Arrays.sort(list);
        ArrayList<String> output = new ArrayList<>();
        for(int i = 0; i < N / 4; i++){
        	output.add(list[i * 4].no + " " + list[i * 4 + 1].no);
        	output.add(list[i * 4 + 1].no + " " + list[i * 4 + 2].no);
        	output.add(list[i * 4 + 2].no + " " + list[i * 4 + 3].no);
        }
        System.out.println(output.size());
        for(int i = 0; i < output.size(); i++){
        	System.out.println(output.get(i));
        }
        System.out.flush();
    }
}
class Node implements Comparable<Node>{
	int no;
	int V;
	Node(int no, int V){
		this.no = no;
		this.V = V;
	}
	public int compareTo(Node ato){
		return this.V - ato.V;
	}
}