#include <iostream>
 #include <ostream>

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

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

       friend constexpr 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 constexpr operator "" _km(long double d){
       return MyDistance(1000*d);
     }
     MyDistance constexpr operator "" _m(long double m){
       return MyDistance(m);
     }
     MyDistance constexpr operator "" _dm(long double d){
       return MyDistance(d/10);
     }
     MyDistance constexpr 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 << "1.5_km + 105.1_m: " << .5_km + 105.1_m << std::endl;

   std::cout << std::endl;

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

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

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

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

 }