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#include <iostream>
#include <vector>

class Number
{
public:
   typedef int Representation;
   class InvalidNumber
   {
   };

   Number();
   Number( const InvalidNumber& invalid );
   explicit Number( const Representation& v );
   friend Number operator + ( const Number& rop, const Number& lop );

   bool operator == ( const Number& v );
   bool operator != ( const Number& v );
   bool operator == ( const Representation& v );
   bool operator != ( const Representation& v );

   bool IsValid() const;
   Representation GetRepresentation() const;
private:
   Representation mValue;
   bool mValid;
};

Number::Number()
   : mValue { 0 },
     mValid { false }
{
}

Number::Number( const Number::InvalidNumber& invalid )
   : mValue { 0 },
     mValid { false }
{
}

Number::Number( const Representation& v )
   : mValue { v },
     mValid { true }
{
}

bool Number::IsValid() const
{
   return mValid;
}

Number::Representation Number::GetRepresentation() const
{
   return mValue;
}

bool Number::operator == ( const Number& v )
{
   return ( v.mValid == mValid ) && ( v.mValue == mValue );
}

bool Number::operator != ( const Number& v )
{
   return ( v.mValid != mValid ) || ( v.mValue != mValue );
}

bool Number::operator == ( const Number::Representation& v )
{
   return ( mValid ) && ( v == mValue );
}

bool Number::operator != ( const Number::Representation& v )
{
   return ( !mValid ) || ( v != mValue );
}

Number operator + ( const Number& rop, const Number& lop )
{
   if( rop.mValid && lop.mValid )
   {
      return Number { rop.mValue + lop.mValue };
   }
   else
   {
      return Number { Number::InvalidNumber() };
   }
}

Number NumberParser( const char* numberString )
{
   const char* p = numberString;
   while( *p != '\0' )
   {
      if( !isdigit( *p ) )
      {
         return Number { Number::InvalidNumber() };
      }
      ++p;
   }
   Number::Representation value = atoi( numberString );
   return Number { value };
}

std::ostream& operator<< ( std::ostream& os, const Number& num )
{
   if( num.IsValid() )
   {
      os << num.GetRepresentation();
   }
   else
   {
      os << "Invalid number";
   }
   return os;
}

class SimpleOperation
{
public:
   typedef Number Result_t;
   typedef Number Parameter_t;
   virtual ~SimpleOperation();
   virtual Result_t operator()( const Parameter_t&, const Parameter_t& ) = 0;
};

SimpleOperation::~SimpleOperation()
{

}

class AssociativeOperation : public SimpleOperation
{
};

class SimpleSum : public AssociativeOperation
{
public:
   virtual Result_t operator()( const Parameter_t&, const Parameter_t& );
};

SimpleSum::Result_t SimpleSum::operator()( const Parameter_t& a, const Parameter_t& b )
{
   Result_t res = a + b;
   return res;
}

class PackOperation
{
public:
   AssociativeOperation::Result_t operator()( const std::vector<AssociativeOperation::Parameter_t>& );
   virtual AssociativeOperation& getOperation() = 0;
};

AssociativeOperation::Result_t PackOperation::operator()( const std::vector<AssociativeOperation::Parameter_t>& parameters )
{
   AssociativeOperation& operation = getOperation();
   AssociativeOperation::Result_t tempResult = AssociativeOperation::Result_t { 0 };

   for( auto param : parameters )
   {
      tempResult = operation( tempResult, param );
   }
   return tempResult;
}

class PackSum : public PackOperation
{
public:
   virtual AssociativeOperation& getOperation();
private:
   SimpleSum mSum;
};

AssociativeOperation& PackSum::getOperation()
{
   return mSum;
}

void print_usage()
{
   std::cout << "Sum operator1 operator2\n";
   std::cout << "print the sum of the operator \n";
}

void print_parsingError( int argIndex )
{
   std::cout << "Error while parsing argument " << argIndex << "\n";
   std::cout << "Aborting...\n";
}

void print_result( Number res )
{
   std::cout << res << "\n";
}

int main( int argc, char* argv[] )
{
   if( argc < 3 )
   {
      print_usage();
      return 1;
   }
   std::vector<Number> addends;
   int opIdx = 1;
   while( opIdx < argc )
   {
      Number n = NumberParser( argv[opIdx] );
      if( n == Number::InvalidNumber() )
      {
         print_parsingError( opIdx );
         return 1;
      }
      addends.push_back( n );
      opIdx++;
   }
   PackOperation* op = new PackSum();
   Number result = ( *op )( addends );
   delete op;
   print_result( result );
   return 0;
}