#include <stdio.h>
#include <stdlib.h>
//#define DEBUG

int* V;
int N;
float P;
int seed;

int cmp(const void* a, const void* b);

int main(int argc, char** argv) {
  int i, j;
  int temp;

  int a, b;

  int length_sum, length_square_sum;

  if ( argc <= 3 ||
       sscanf(argv[1], " %d", &N) != 1 ||
       sscanf(argv[2], " %f", &P) != 1 ||
       sscanf(argv[3], " %d", &seed) != 1 ) {
    fprintf(stderr, "uso: %s N P seed\n", argv[0], N, P, seed);
    exit(1);
  }

  srand(seed);

  V = (int*) calloc (2 * N, sizeof(int));

  /* Spostamento casuale */
  for ( i = 0 ; i < 2 * N ; i++ )
    V[i] = i;

  for ( i = 0 ; i < 2 * N ; i++ ) {
    for ( j = i ; (rand() * 1.0) / RAND_MAX < P ; j++ )
      if ( j == 2 * N - 1 )
	break;
    
    temp = V[i];
    V[i] = V[j];
    V[j] = temp;

  }

  /* Ordinamento elementi coppia */
  for ( i = 0 ; i < N ; i++ )
    if ( V[2 * i] > V[2 * i + 1] ) {
      temp = V[2 * i];
      V[2 * i] = V[2 * i + 1];
      V[2 * i + 1] = temp;
    }

  /* Ordinamento coppie */
  qsort(V, N, 2 * sizeof(int), cmp);

  /* Stampa */
#ifdef DEBUG

  length_sum = 0;
  length_square_sum = 0;
  for ( i = 0 ; i < N ; i++ ) {
    length_sum += V[2 * i + 1] - V[2 * i];
    length_square_sum += (V[2 * i + 1] - V[2 * i]) * (V[2 * i + 1] - V[2 * i]);

    fprintf(stderr, "%4d (%4d, %4d) |", i, V[2 * i], V[2 * i + 1]);

    for ( j = 0 ; j < 2 * N ; j++ )
      if ( j < V[2 * i] || j > V[2 * i + 1] )
	fprintf(stderr, " ");
      else
	fprintf(stderr, "*");
    
    fprintf(stderr, "|\n");
  }
  fprintf(stderr, "Lunghezza media: %f\n", (length_sum * 1.0) / N);
  fprintf(stderr, "Varianza: %f\n", (length_square_sum * 1.0) / N - ((length_sum * 1.0) / N) * ((length_sum * 1.0) / N));

#endif

  printf("%d\n", N);
  for ( i = 0 ; i < N ; i++ )
    printf("%d %d\n", V[2 * i], V[2 * i + 1]);

  return 0;
}

int cmp(const void* a, const void* b) {
  int* A = (int*) a;
  int* B = (int*) b;

  return A[0] - B[0];
}