#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

typedef struct levels {
  size_t mem_size;
  size_t size;
  unsigned int *data;
} levels_t;

int main(void) {
  FILE *fp = fopen("example", "r");

  if (fp == NULL) {
    perror("input");
    return 1;
  }

  char *line = NULL;
  size_t size;

  levels_t levels;
  levels.mem_size = 10;
  levels.size = 0;
  levels.data = malloc(sizeof(unsigned int) * levels.mem_size);

  unsigned int sum = 0;
  while (getline(&line, &size, fp) > 0) {
    char *next = strtok(line, " ");

    while (next != NULL) {
      if (levels.size >= levels.mem_size) {
        levels.mem_size *= 2;
        levels.data =
            realloc(levels.data, levels.mem_size * sizeof(unsigned int));
      }

      sscanf(next, "%u", &levels.data[levels.size]);
      levels.size++;

      next = strtok(NULL, " ");
    }

    bool removed_node = false;
    bool safe = true;
    int diff = levels.data[1] - levels.data[0];
    int increasing = diff > 0 ? 1 : -1;
    for (int i = 1; i < levels.size; i++) {
      diff = increasing * (levels.data[i] - levels.data[i - 1]);

      if (diff < 1 || diff > 3) {
        if (removed_node) {
          safe = false;
          break;
        }
        for (int j = i; j < levels.size; j++) {
          levels.data[j - 1] = levels.data[j];
        }
        levels.size--;
        i = 0;
        removed_node = true;
      }
    }

    if (safe) {
      sum++;
    }

    levels.size = 0;
  }

  free(line);
  free(levels.data);

  printf("%u\n", sum);

  fclose(fp);

  return 0;
}