#include <iostream>
#include <vector>
#include <set>



//          Copyright Louis Delacroix 2010 - 2014.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)
//
// A pretty printing library for C++
//
// Usage:
// Include this header, and operator<< will "just work".

#ifndef H_PRETTY_PRINT
#define H_PRETTY_PRINT

#include <cstddef>
#include <iterator>
#include <memory>
#include <ostream>
#include <set>
#include <tuple>
#include <type_traits>
#include <unordered_set>
#include <utility>
#include <valarray>

namespace pretty_print
{
    namespace detail
    {
        // SFINAE type trait to detect whether T::const_iterator exists.

        struct sfinae_base
        {
            using yes = char;
            using no  = yes[2];
        };

        template <typename T>
        struct has_const_iterator : private sfinae_base
        {
        private:
            template <typename C> static yes & test(typename C::const_iterator*);
            template <typename C> static no  & test(...);
        public:
            static const bool value = sizeof(test<T>(nullptr)) == sizeof(yes);
            using type =  T;
        };

        template <typename T>
        struct has_begin_end : private sfinae_base
        {
        private:
            template <typename C>
            static yes & f(typename std::enable_if<
                std::is_same<decltype(static_cast<typename C::const_iterator(C::*)() const>(&C::begin)),
                             typename C::const_iterator(C::*)() const>::value>::type *);

            template <typename C> static no & f(...);

            template <typename C>
            static yes & g(typename std::enable_if<
                std::is_same<decltype(static_cast<typename C::const_iterator(C::*)() const>(&C::end)),
                             typename C::const_iterator(C::*)() const>::value, void>::type*);

            template <typename C> static no & g(...);

        public:
            static bool const beg_value = sizeof(f<T>(nullptr)) == sizeof(yes);
            static bool const end_value = sizeof(g<T>(nullptr)) == sizeof(yes);
        };

    }  // namespace detail


    // Holds the delimiter values for a specific character type

    template <typename TChar>
    struct delimiters_values
    {
        using char_type = TChar;
        const char_type * prefix;
        const char_type * delimiter;
        const char_type * postfix;
    };


    // Defines the delimiter values for a specific container and character type

    template <typename T, typename TChar>
    struct delimiters
    {
        using type = delimiters_values<TChar>;
        static const type values;
    };


    // Functor to print containers. You can use this directly if you want
    // to specificy a non-default delimiters type. The printing logic can
    // be customized by specializing the nested template.

    template <typename T,
              typename TChar = char,
              typename TCharTraits = ::std::char_traits<TChar>,
              typename TDelimiters = delimiters<T, TChar>>
    struct print_container_helper
    {
        using delimiters_type = TDelimiters;
        using ostream_type = std::basic_ostream<TChar, TCharTraits>;

        template <typename U>
        struct printer
        {
            static void print_body(const U & c, ostream_type & stream)
            {
                using std::begin;
                using std::end;

                auto it = begin(c);
                const auto the_end = end(c);

                if (it != the_end)
                {
                    for ( ; ; )
                    {
                        stream << *it;

                    if (++it == the_end) break;

                    if (delimiters_type::values.delimiter != NULL)
                        stream << delimiters_type::values.delimiter;
                    }
                }
            }
        };

        print_container_helper(const T & container)
        : container_(container)
        { }

        inline void operator()(ostream_type & stream) const
        {
            if (delimiters_type::values.prefix != NULL)
                stream << delimiters_type::values.prefix;

            printer<T>::print_body(container_, stream);

            if (delimiters_type::values.postfix != NULL)
                stream << delimiters_type::values.postfix;
        }

    private:
        const T & container_;
    };

    // Specialization for pairs

    template <typename T, typename TChar, typename TCharTraits, typename TDelimiters>
    template <typename T1, typename T2>
    struct print_container_helper<T, TChar, TCharTraits, TDelimiters>::printer<std::pair<T1, T2>>
    {
        using ostream_type = typename print_container_helper<T, TChar, TCharTraits, TDelimiters>::ostream_type;

        static void print_body(const std::pair<T1, T2> & c, ostream_type & stream)
        {
            stream << c.first;
            if (print_container_helper<T, TChar, TCharTraits, TDelimiters>::delimiters_type::values.delimiter != NULL)
                stream << print_container_helper<T, TChar, TCharTraits, TDelimiters>::delimiters_type::values.delimiter;
            stream << c.second;
        }
    };

    // Specialization for tuples

    template <typename T, typename TChar, typename TCharTraits, typename TDelimiters>
    template <typename ...Args>
    struct print_container_helper<T, TChar, TCharTraits, TDelimiters>::printer<std::tuple<Args...>>
    {
        using ostream_type = typename print_container_helper<T, TChar, TCharTraits, TDelimiters>::ostream_type;
        using element_type = std::tuple<Args...>;

        template <std::size_t I> struct Int { };

        static void print_body(const element_type & c, ostream_type & stream)
        {
            tuple_print(c, stream, Int<0>());
        }

        static void tuple_print(const element_type &, ostream_type &, Int<sizeof...(Args)>)
        {
        }

        static void tuple_print(const element_type & c, ostream_type & stream,
                                typename std::conditional<sizeof...(Args) != 0, Int<0>, std::nullptr_t>::type)
        {
            stream << std::get<0>(c);
            tuple_print(c, stream, Int<1>());
        }

        template <std::size_t N>
        static void tuple_print(const element_type & c, ostream_type & stream, Int<N>)
        {
            if (print_container_helper<T, TChar, TCharTraits, TDelimiters>::delimiters_type::values.delimiter != NULL)
                stream << print_container_helper<T, TChar, TCharTraits, TDelimiters>::delimiters_type::values.delimiter;

            stream << std::get<N>(c);

            tuple_print(c, stream, Int<N + 1>());
        }
    };

    // Prints a print_container_helper to the specified stream.

    template<typename T, typename TChar, typename TCharTraits, typename TDelimiters>
    inline std::basic_ostream<TChar, TCharTraits> & operator<<(
        std::basic_ostream<TChar, TCharTraits> & stream,
        const print_container_helper<T, TChar, TCharTraits, TDelimiters> & helper)
    {
        helper(stream);
        return stream;
    }


    // Basic is_container template; specialize to derive from std::true_type for all desired container types

    template <typename T>
    struct is_container : public std::integral_constant<bool,
                                                        detail::has_const_iterator<T>::value &&
                                                        detail::has_begin_end<T>::beg_value  &&
                                                        detail::has_begin_end<T>::end_value> { };

    template <typename T, std::size_t N>
    struct is_container<T[N]> : std::true_type { };

    template <std::size_t N>
    struct is_container<char[N]> : std::false_type { };

    template <typename T>
    struct is_container<std::valarray<T>> : std::true_type { };

    template <typename T1, typename T2>
    struct is_container<std::pair<T1, T2>> : std::true_type { };

    template <typename ...Args>
    struct is_container<std::tuple<Args...>> : std::true_type { };


    // Default delimiters

    template <typename T> struct delimiters<T, char> { static const delimiters_values<char> values; };
    template <typename T> const delimiters_values<char> delimiters<T, char>::values = { "[", ", ", "]" };
    template <typename T> struct delimiters<T, wchar_t> { static const delimiters_values<wchar_t> values; };
    template <typename T> const delimiters_values<wchar_t> delimiters<T, wchar_t>::values = { L"[", L", ", L"]" };


    // Delimiters for (multi)set and unordered_(multi)set

    template <typename T, typename TComp, typename TAllocator>
    struct delimiters< ::std::set<T, TComp, TAllocator>, char> { static const delimiters_values<char> values; };

    template <typename T, typename TComp, typename TAllocator>
    const delimiters_values<char> delimiters< ::std::set<T, TComp, TAllocator>, char>::values = { "{", ", ", "}" };

    template <typename T, typename TComp, typename TAllocator>
    struct delimiters< ::std::set<T, TComp, TAllocator>, wchar_t> { static const delimiters_values<wchar_t> values; };

    template <typename T, typename TComp, typename TAllocator>
    const delimiters_values<wchar_t> delimiters< ::std::set<T, TComp, TAllocator>, wchar_t>::values = { L"{", L", ", L"}" };

    template <typename T, typename TComp, typename TAllocator>
    struct delimiters< ::std::multiset<T, TComp, TAllocator>, char> { static const delimiters_values<char> values; };

    template <typename T, typename TComp, typename TAllocator>
    const delimiters_values<char> delimiters< ::std::multiset<T, TComp, TAllocator>, char>::values = { "{", ", ", "}" };

    template <typename T, typename TComp, typename TAllocator>
    struct delimiters< ::std::multiset<T, TComp, TAllocator>, wchar_t> { static const delimiters_values<wchar_t> values; };

    template <typename T, typename TComp, typename TAllocator>
    const delimiters_values<wchar_t> delimiters< ::std::multiset<T, TComp, TAllocator>, wchar_t>::values = { L"{", L", ", L"}" };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    struct delimiters< ::std::unordered_set<T, THash, TEqual, TAllocator>, char> { static const delimiters_values<char> values; };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    const delimiters_values<char> delimiters< ::std::unordered_set<T, THash, TEqual, TAllocator>, char>::values = { "{", ", ", "}" };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    struct delimiters< ::std::unordered_set<T, THash, TEqual, TAllocator>, wchar_t> { static const delimiters_values<wchar_t> values; };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    const delimiters_values<wchar_t> delimiters< ::std::unordered_set<T, THash, TEqual, TAllocator>, wchar_t>::values = { L"{", L", ", L"}" };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    struct delimiters< ::std::unordered_multiset<T, THash, TEqual, TAllocator>, char> { static const delimiters_values<char> values; };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    const delimiters_values<char> delimiters< ::std::unordered_multiset<T, THash, TEqual, TAllocator>, char>::values = { "{", ", ", "}" };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    struct delimiters< ::std::unordered_multiset<T, THash, TEqual, TAllocator>, wchar_t> { static const delimiters_values<wchar_t> values; };

    template <typename T, typename THash, typename TEqual, typename TAllocator>
    const delimiters_values<wchar_t> delimiters< ::std::unordered_multiset<T, THash, TEqual, TAllocator>, wchar_t>::values = { L"{", L", ", L"}" };


    // Delimiters for pair and tuple

    template <typename T1, typename T2> struct delimiters<std::pair<T1, T2>, char> { static const delimiters_values<char> values; };
    template <typename T1, typename T2> const delimiters_values<char> delimiters<std::pair<T1, T2>, char>::values = { "(", ", ", ")" };
    template <typename T1, typename T2> struct delimiters< ::std::pair<T1, T2>, wchar_t> { static const delimiters_values<wchar_t> values; };
    template <typename T1, typename T2> const delimiters_values<wchar_t> delimiters< ::std::pair<T1, T2>, wchar_t>::values = { L"(", L", ", L")" };

    template <typename ...Args> struct delimiters<std::tuple<Args...>, char> { static const delimiters_values<char> values; };
    template <typename ...Args> const delimiters_values<char> delimiters<std::tuple<Args...>, char>::values = { "(", ", ", ")" };
    template <typename ...Args> struct delimiters< ::std::tuple<Args...>, wchar_t> { static const delimiters_values<wchar_t> values; };
    template <typename ...Args> const delimiters_values<wchar_t> delimiters< ::std::tuple<Args...>, wchar_t>::values = { L"(", L", ", L")" };


    // Type-erasing helper class for easy use of custom delimiters.
    // Requires TCharTraits = std::char_traits<TChar> and TChar = char or wchar_t, and MyDelims needs to be defined for TChar.
    // Usage: "cout << pretty_print::custom_delims<MyDelims>(x)".

    struct custom_delims_base
    {
        virtual ~custom_delims_base() { }
        virtual std::ostream & stream(::std::ostream &) = 0;
        virtual std::wostream & stream(::std::wostream &) = 0;
    };

    template <typename T, typename Delims>
    struct custom_delims_wrapper : custom_delims_base
    {
        custom_delims_wrapper(const T & t_) : t(t_) { }

        std::ostream & stream(std::ostream & s)
        {
            return s << print_container_helper<T, char, std::char_traits<char>, Delims>(t);
        }

        std::wostream & stream(std::wostream & s)
        {
            return s << print_container_helper<T, wchar_t, std::char_traits<wchar_t>, Delims>(t);
        }

    private:
        const T & t;
    };

    template <typename Delims>
    struct custom_delims
    {
        template <typename Container>
        custom_delims(const Container & c) : base(new custom_delims_wrapper<Container, Delims>(c)) { }

        std::unique_ptr<custom_delims_base> base;
    };

    template <typename TChar, typename TCharTraits, typename Delims>
    inline std::basic_ostream<TChar, TCharTraits> & operator<<(std::basic_ostream<TChar, TCharTraits> & s, const custom_delims<Delims> & p)
    {
        return p.base->stream(s);
    }


    // A wrapper for a C-style array given as pointer-plus-size.
    // Usage: std::cout << pretty_print_array(arr, n) << std::endl;

    template<typename T>
    struct array_wrapper_n
    {
        typedef const T * const_iterator;
        typedef T value_type;

        array_wrapper_n(const T * const a, size_t n) : _array(a), _n(n) { }
        inline const_iterator begin() const { return _array; }
        inline const_iterator end() const { return _array + _n; }

    private:
        const T * const _array;
        size_t _n;
    };


    // A wrapper for hash-table based containers that offer local iterators to each bucket.
    // Usage: std::cout << bucket_print(m, 4) << std::endl;  (Prints bucket 5 of container m.)

    template <typename T>
    struct bucket_print_wrapper
    {
        typedef typename T::const_local_iterator const_iterator;
        typedef typename T::size_type size_type;

        const_iterator begin() const
        {
            return m_map.cbegin(n);
        }

        const_iterator end() const
        {
            return m_map.cend(n);
        }

        bucket_print_wrapper(const T & m, size_type bucket) : m_map(m), n(bucket) { }

    private:
        const T & m_map;
        const size_type n;
    };

}   // namespace pretty_print


// Global accessor functions for the convenience wrappers

template<typename T>
inline pretty_print::array_wrapper_n<T> pretty_print_array(const T * const a, size_t n)
{
    return pretty_print::array_wrapper_n<T>(a, n);
}

template <typename T> pretty_print::bucket_print_wrapper<T>
bucket_print(const T & m, typename T::size_type n)
{
    return pretty_print::bucket_print_wrapper<T>(m, n);
}


// Main magic entry point: An overload snuck into namespace std.
// Can we do better?

namespace std
{
    // Prints a container to the stream using default delimiters

    template<typename T, typename TChar, typename TCharTraits>
    inline typename enable_if< ::pretty_print::is_container<T>::value,
                              basic_ostream<TChar, TCharTraits> &>::type
    operator<<(basic_ostream<TChar, TCharTraits> & stream, const T & container)
    {
        return stream << ::pretty_print::print_container_helper<T, TChar, TCharTraits>(container);
    }
}

#endif  // H_PRETTY_PRINT

using namespace std;

using LR = pair<long, long>;

class LeftCompare {
public:
    bool operator() (const LR &lhs, const LR &rhs) {
        return lhs.first > rhs.first ||
            lhs.first == rhs.first && lhs.second > rhs.second;
    }
};

class RightCompare {
public:
    bool operator() (const LR &lhs, const LR &rhs) {
        return lhs.second < rhs.second ||
                            lhs.second == rhs.second &&
                            lhs.first < rhs.first;
    }
};

class Ranges {
    multiset<LR, LeftCompare> lefts;
    multiset<LR, RightCompare> rights;

public:
    Ranges(const vector<LR> &ranges) :
        lefts(ranges.begin(), ranges.end()),
        rights(ranges.begin(), ranges.end()) {}

    LR pop_left() {
        //        cerr << "popping left" << endl;
        auto first = lefts.begin();
        LR ret = *first;
        lefts.erase(first);
        rights.erase(rights.find(ret));
        return ret;
    }

    LR pop_right() {
        //        cerr << "popping right" << endl;
        auto first = rights.begin();
        LR ret = *first;
        rights.erase(first);
        auto left_found = lefts.find(ret);
        // cerr << "left: " << *left_found << endl;
        // cerr << "ret: " << ret << endl;
        lefts.erase(lefts.find(ret));
        return ret;
    }

    LR pop(bool left) {
        return left ? pop_left() : pop_right();
    }

    friend ostream &operator<<(ostream &os, const Ranges &ranges);
};

ostream &operator<<(ostream &os, const Ranges &ranges) {
    os << ranges.lefts << "," << ranges.rights << endl;
    return os;
}

long calc(const vector<LR> &ranges, bool left) {
    Ranges world(ranges);
    long current = 0;
    long ret = 0;
    for(long i=0; i<ranges.size(); i++) {
        // cerr << i << ": " << endl;
        LR pair = world.pop(left);
        // cerr << "popped: " << pair << endl;
        // cerr << "world: " << world << endl;
        if(left) {
            if (current < pair.first) {
                ret += pair.first - current;
                current = pair.first;
            }
        } else {
            if (current > pair.second) {
                ret += current - pair.second;
                current = pair.second;
            }
        }
        left = !left;
    }
    ret += abs(current);
    return ret;
}

int main() {
    long N;
    cin >> N;
    vector<LR> ranges;
    for(long i=0; i<N; i++){
        long l, r;
        cin >> l >> r;
        ranges.push_back(make_pair(l, r));
    }

    // cerr << "start calc v1" << endl;
    long v1 = calc(ranges, true);
    long v2 = calc(ranges, false);

    // cerr << "v1:" << v1 << endl;
    // cerr << "v2:" << v2 << endl;

    cout << max(v1, v2) << endl;
}


Measured memory_bytes: 14320