import java.util.*;

public class RandomSMForbidden { 

    static Random gen;    

    static void shuffle(ArrayList<Object> v){
	int j,n;
	n = v.size();
	Object temp;
	for (int i=n-1;i>0;i--){
	    j = gen.nextInt(i+1);
	    temp = v.get(i);
	    v.set(i,v.get(j));
	    v.set(j,temp);
	}
    }

    static Edge randomSelect(ArrayList<Edge> v){
	if (v.isEmpty()) return null;
	return v.get(gen.nextInt(v.size()));
    }

    public static void main(String[] args) throws Exception {
	gen               = new Random();
	int n             = Integer.parseInt(args[0]);
	double p          = 1.0; // probability of an edge
	double pForbidden = 0.0; // probability that a selected edge is forbidden
	ArrayList[] V     = new ArrayList[n];
	ArrayList<Edge> E = new ArrayList<Edge>();
	ArrayList<Integer> agent = new ArrayList<Integer>(n);
	int forbidden = 0;
	for (int i=0;i<n;i++) V[i] = new ArrayList<Integer>();	    
	if (args.length >= 2) p = Double.parseDouble(args[1]);
	System.out.println(n);
	for (int i=0;i<n/2;i++)
	    for (int j=n/2;j<n;j++)
		if (p >= gen.nextDouble()){
		    V[i].add(j);
		    V[j].add(i);
		    E.add(new Edge(i,j));
		}
	for (int i=0;i<n;i++){
	    shuffle(V[i]);
	    for (int j : (ArrayList<Integer>)V[i]) System.out.print((j+1) +" ");
	    System.out.println();
	}
	if (args.length >= 3){
	    pForbidden = Double.parseDouble(args[2]);
	    for (Edge e : E) 
		if (pForbidden >= gen.nextDouble()){
		    System.out.println("forbidden "+ (e.v+1) +" "+ (e.w+1));
		    forbidden++;
		}
	}
	//System.out.println("selected: " + E.size() + " forbidden: "+ forbidden);
    }
}