struct DefaultType{};

template<class T>
struct Holder {
    Holder();
    Holder(const Holder<DefaultType>&);
};

template<class T>
int check_type( 
  Holder<T> a=Holder<DefaultType>(), 
  Holder<T> b=Holder<DefaultType>(), 
  Holder<T> c=Holder<DefaultType>(), 
  Holder<T> d=Holder<DefaultType>(),
  Holder<T> e=Holder<DefaultType>() );


template<
    class T1=DefaultType, class T2=DefaultType, class T3=DefaultType, 
    class T4=DefaultType, class T5=DefaultType>
struct CommonType {
    enum { Check = sizeof( check_type<T1>( Holder<T2>(), Holder<T3>(), 
                                Holder<T4>(), Holder<T5>() ) ) };
    typedef T1 Type;
    
};

template<class T2, class T3, class T4, class T5>
struct CommonType<DefaultType, T2, T3, T4, T5> {
    enum { Check = sizeof( check_type<T2>( Holder<T3>(), Holder<T4>(), 
                                    Holder<T5>() ) ) };
    typedef T2 Type;
};

template<class T3, class T4, class T5>
struct CommonType<DefaultType, DefaultType, T3, T4, T5> {
    enum { Check = sizeof( check_type<T3>( Holder<T4>(), Holder<T5>() ) ) };
    typedef T3 Type;
    
};

template<class T4, class T5>
struct CommonType<DefaultType, DefaultType, DefaultType, T4, T5> {
    enum { Check = sizeof( check_type<T4>( Holder<T5>() ) ) };
    typedef T4 Type;    
};

template<class T5>
struct CommonType<DefaultType, DefaultType, DefaultType, DefaultType, T5> {
    typedef T5 Type;    
};


template<>
struct CommonType<> {
    typedef DefaultType Type;
};