double straightforward( std::vector< int >& v1, std::vector< int >& v2 )
    {
        if( v1.empty() && v2.empty() )
        {
            return NAN;
        }

        size_t i = v1.size();
        size_t j = v2.size();
        const size_t n = i + j;
        size_t m = n / 2 + 1;

        int mid[ 2 ]{};
        int mid_idx = 0;

        for( ; i && j && m; --m )
        {
            auto& a = v1[ i - 1 ];
            auto& b = v2[ j - 1 ];

            if( a >= b )
            {
                mid[ mid_idx ] = a;
                --i;
            }
            else
            {
                mid[ mid_idx ] = b;
                --j;
            }

            mid_idx = 1 - mid_idx;
        }

        if( m )
        {
            auto& v = i ? v1 : v2;
            auto k = i ? i : j;

            if( m == 1 )
            {
                mid[ mid_idx ] = v[ k - 1 ];
                mid_idx = 1 - mid_idx;
            }
            else
            {
                k -= m;
                mid[ 1 - mid_idx ] = v[ k ];
                mid[ mid_idx ] = v[ k + 1 ];
            }
        }

        if( n % 2 == 1 )
        {
            return mid[ 1 - mid_idx ];
        }

        return ( mid[ 0 ] + mid[ 1 ] ) / 2.0;
    }