    <?php
    $apex = [];
    $operation = 0;

    $node = trim(fgets(STDIN));
    for ($i = 0; $i < $node; ++$i) {
      $string_array = explode(" ", trim(fgets(STDIN)));
      if (isset($string_array[ $value[0] ])) $string_array[ $value[0] ]++;
      else $string_array[ $value[0] ] = 1;
      if (isset($string_array[ $value[1] ])) $string_array[ $value[1] ]++;
      else $string_array[ $value[1] ] = 1;
    }

    $side_num = array_count_values($apex);
    while ($side_num[1] > 2) {
      $operation++;
      $side_num[1]--;
    }
    echo $operation;