text: constexpr unsigned long long binary_helper(unsigned long long digits,
                                             unsigned long long result,
                                             int shift)
  {
      return 0 == digits 
             ? result
             : binary_helper(digits / 10,
                             result | ((digits % 10 == 1) << shift),
                             digits % 10 < 2 ? shift + 1 : shift);
  }
  
  constexpr unsigned long long operator"" _binary(unsigned long long digits)
  {
      return binary_helper(digits, 0ULL, 0);
  }
  
  #include <iostream>
  int main() {
      std::cout << 11_binary << std::endl;
  
      return 0;
  }
  