#include <iostream>
 #include <ostream>

 namespace Distance{
   class MyDistance{
     public:
       MyDistance(double i):m(i){}

       friend MyDistance operator+(const MyDistance& a, const MyDistance& b){
         return MyDistance(a.m + b.m);
       }

       friend MyDistance operator-(const MyDistance& a, const MyDistance& b){
         return MyDistance(a.m - b.m);
       }

       friend MyDistance operator*(double m, const MyDistance& a){
         return MyDistance(m*a.m);
       }

       friend std::ostream& operator<<(std::ostream &out, const MyDistance& myDist){
         out << myDist.m << " m";
         return out;
       }
     private:
       double m;
   };

   namespace Unit{
     MyDistance operator "" _km(long double d){
       return MyDistance(1000*d);
     }
     MyDistance operator "" _m(long double m){
       return MyDistance(m);
     }
     MyDistance operator "" _dm(long double d){
       return MyDistance(d/10);
     }
     MyDistance operator "" _cm(long double c){
       return MyDistance(c/100);
     }
   }
 }

 using namespace Distance::Unit;

 int main(){

   std:: cout << std::endl;

   std::cout << "1.0_km: " << 1.0_km << std::endl;
   std::cout << "1.0_m: " << 1.0_m << std::endl;
   std::cout << "1.0_dm: " << 1.0_dm << std::endl;
   std::cout << "1.0_cm: " << 1.0_cm << std::endl;

   std::cout << std::endl;

   std::cout << "0.001 * 1.0_km: " << 0.001 * 1.0_km << std::endl;
   std::cout << "10 * 1_dm: " << 10 * 1.0_dm << std::endl;
   std::cout << "100 * 1.0cm: " << 100 * 1.0_cm << std::endl;

   std::cout << std::endl;
   std::cout << "1.0_km + 2.0_dm +  3.0_dm + 4.0_cm: " << 1.0_km + 2.0_dm +  3.0_dm + 4.0_cm << std::endl;
   std::cout << std::endl;

   Distance::MyDistance work= 63.0_km;
   Distance::MyDistance workPerDay= 2 * work;
   Distance::MyDistance abbrevationToWork= 5400.0_m;
   Distance::MyDistance workout= 2 * 1600.0_m;
   Distance::MyDistance shopping= 2 * 1200.0_m;

   Distance::MyDistance myDistancePerWeek= 4 * workPerDay - 3 * abbrevationToWork + workout + shopping;

   std::cout << "4 * workPerDay - 3 * abbrevationToWork + workout + shopping: " << myDistancePerWeek;

   std::cout << "\n\n";

 }