Language: C++

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 10;
typedef long long ll;
int n, x, l[maxn], r[maxn];
ll ans1, ans2;
struct cmpl { bool operator () (const int & i, const int & j) { return l[i] > l[j] || (l[i] == l[j] && i < j);}};
struct cmpr { bool operator () (const int & i, const int & j) { return r[i] < r[j] || (r[i] == r[j] && i < j);}};
set<int, cmpl> sl;
set<int, cmpr> sr;
int main()
{
	scanf("%d", &n);
	for(int i = 1; i <= n; ++i)
	{
		scanf("%d%d", &l[i], &r[i]);
		sl.insert(i); sr.insert(i);
	}
	int cur = 0;
	for(int i = 1; i <= n; ++i)
	{
		if(i & 1) x = *sl.begin();
		else x = *sr.begin();
		sl.erase(x); sr.erase(x);
		if(l[x] <= cur && cur <= r[x]) continue;
		else if(cur < l[x]) { ans1 += l[x] - cur; cur = l[x];}
		else { ans1 += cur - r[x]; cur = r[x];}
	}
	ans1 += abs(cur);
	
	for(int i = 1; i <= n; ++i) sl.insert(i), sr.insert(i);
	cur = 0;
	for(int i = 1; i <= n; ++i)
	{
		if(i & 1) x = *sl.begin();
		else x = *sr.begin();
		sl.erase(x); sr.erase(x);
		if(l[x] <= cur && cur <= r[x]) continue;
		else if(cur < l[x]) { ans2 += l[x] - cur; cur = l[x];}
		else { ans2 += cur - r[x]; cur = r[x];}
	}
	ans2 += abs(cur);
	
	cout << max(ans1, ans2) << endl;
	return 0;
}

Compiler output:
In file included from /usr/include/c++/14/map:62,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_tree.h: In instantiation of 'static const _Key& std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_S_key(_Const_Link_type) [with _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = cmpl; _Alloc = std::allocator<int>; _Const_Link_type = const std::_Rb_tree_node<int>*]':
/usr/include/c++/14/bits/stl_tree.h:2116:47:   required from 'std::pair<std::_Rb_tree_node_base*, std::_Rb_tree_node_base*> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_get_insert_unique_pos(const key_type&) [with _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = cmpl; _Alloc = std::allocator<int>; key_type = int]'
 2116 |           __comp = _M_impl._M_key_compare(__k, _S_key(__x));
      |                                                ~~~~~~^~~~~
/usr/include/c++/14/bits/stl_tree.h:2169:4:   required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = const int&; _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = cmpl; _Alloc = std::allocator<int>]'
 2169 |         = _M_get_insert_unique_pos(_KeyOfValue()(__v));
      |           ^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_set.h:514:25:   required from 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(const value_type&) [with _Key = int; _Compare = cmpl; _Alloc = std::allocator<int>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree<int, int, std::_Identity<int>, cmpl, std::allocator<int> >::const_iterator; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other = std::allocator<int>; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key> = __gnu_cxx::__alloc_traits<std::allocator<int>, int>::rebind<int>; typename _Alloc::value_type = int; value_type = int]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:17:12:   required from here
   17 |                 sl.insert(i); sr.insert(i);
      |                 ~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_tree.h:768:15: error: static assertion failed: comparison object must be invocable as const
  768 |               is_invocable_v<const _Compare&, const _Key&, const _Key&>,
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:768:15: note: 'std::is_invocable_v<const cmpl&, const int&, const int&>' evaluates to false
/usr/include/c++/14/bits/stl_tree.h: In instantiation of 'static const _Key& std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_S_key(_Const_Link_type) [with _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = cmpr; _Alloc = std::allocator<int>; _Const_Link_type = const std::_Rb_tree_node<int>*]':
/usr/include/c++/14/bits/stl_tree.h:2116:47:   required from 'std::pair<std::_Rb_tree_node_base*, std::_Rb_tree_node_base*> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_get_insert_unique_pos(const key_type&) [with _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = cmpr; _Alloc = std::allocator<int>; key_type = int]'
 2116 |           __comp = _M_impl._M_key_compare(__k, _S_key(__x));
      |                                                ~~~~~~^~~~~
/usr/include/c++/14/bits/stl_tree.h:2169:4:   required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = const int&; _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = cmpr; _Alloc = std::allocator<int>]'
 2169 |         = _M_get_insert_unique_pos(_KeyOfValue()(__v));
      |           ^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_set.h:514:25:   required from 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(const value_type&) [with _Key = int; _Compare = cmpr; _Alloc = std::allocator<int>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree<int, int, std::_Identity<int>, cmpr, std::allocator<int> >::const_iterator; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other = std::allocator<int>; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key> = __gnu_cxx::__alloc_traits<std::allocator<int>, int>::rebind<int>; typename _Alloc::value_type = int; value_type = int]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:17:26:   required from here
   17 |                 sl.insert(i); sr.insert(i);
      |                               ~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_tree.h:768:15: error: static assertion failed: comparison object must be invocable as const
  768 |               is_invocable_v<const _Compare&, const _Key&, const _Key&>,
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:768:15: note: 'std::is_invocable_v<const cmpr&, const int&, const int&>' evaluates to false