text: #include <algorithm>
  #include <cassert>
  #include <iostream>
  #include <string>
  
  // Merge two strings of answers, preserving order and ensuring uniqueness of
  // each answer.
  std::string merge_answers(std::string const &a, std::string const &b) {
    std::string result;
    std::string::size_type pos_a = 0;
    std::string::size_type pos_b = 0;
    while (pos_a < a.length() && pos_b < b.length()) {
      if (a[pos_a] < b[pos_b]) {
        result += a[pos_a];
        ++pos_a;
      } else if (b[pos_b] < a[pos_a]) {
        result += b[pos_b];
        ++pos_b;
      } else {
        assert(a[pos_a] == b[pos_b]);
        result += a[pos_a];
        ++pos_a;
        ++pos_b;
      }
    }
    result += a.substr(pos_a);
    result += b.substr(pos_b);
    std::cout << "Merged " << a << " and " << b << " to " << result << "\n";
    return result;
  }
  
  int main(int argc, char **argv) {
  
    std::string current_answers;
    unsigned count = 0;
    for (std::string line; std::getline(std::cin, line);) {
      if (!line.empty()) {
        std::sort(line.begin(), line.end());
        current_answers = merge_answers(current_answers, line);
      } else {
        std::cout << "Length of " << current_answers << " = "
                  << current_answers.length() << "\n";
        count += current_answers.length();
        current_answers.clear();
      }
    }
    std::cout << "Length of " << current_answers << " = "
              << current_answers.length() << "\n";
    count += current_answers.length();
  
    std::cout << "Total length = " << count << "\n";
    return 0;
  }