Language: C++

#include <iostream>
#include <algorithm>
#include <utility>
#include <tuple>
#include <vector>
#include <list>

        int N, M;

std::list<std::pair<int, int>> ab;

int main()
{
        std::cin >> N >> M;
        for (int i = 0; i < M; ++i) {
                int a, b;
                std::cin >> a >> b;
                ab.push_back({a, b});
        }
        std::sort(ab.begin(), ab.end(), [](const std::pair<int, int>& x, const std::pair<int, int>& y) { if (x.second < y.second) return true; return (x.first < y.first);});

        int n = 0;
        while (!ab.empty()) {
                ++n;
                auto x = ab.front();
                auto it = std::remove_if(ab.begin(), ab.end(), [&x](const std::pair<int, int>& y){ return y.first < x.second; });
                ab.erase(it ,ab.end());
        }
        std::cout << n << "\n";

        return 0;
}

Compiler output:
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_algo.h: In instantiation of 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = _List_iterator<pair<int, int> >; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<main()::<lambda(const pair<int, int>&, const pair<int, int>&)> >]':
/usr/include/c++/14/bits/stl_algo.h:4805:18:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = _List_iterator<pair<int, int> >; _Compare = main()::<lambda(const pair<int, int>&, const pair<int, int>&)>]'
 4805 |       std::__sort(__first, __last, __gnu_cxx::__ops::__iter_comp_iter(__comp));
      |       ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:20:18:   required from here
   20 |         std::sort(ab.begin(), ab.end(), [](const std::pair<int, int>& x, const std::pair<int, int>& y) { if (x.second < y.second) return true; return (x.first < y.first);});
      |         ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1906:50: error: no match for 'operator-' (operand types are 'std::_List_iterator<std::pair<int, int> >' and 'std::_List_iterator<std::pair<int, int> >')
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
In file included from /usr/include/c++/14/string:48,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_iterator.h:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_List_iterator<std::pair<int, int> >' is not derived from 'const std::reverse_iterator<_Iterator>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_algo.h:1906:50: note:   'std::_List_iterator<std::pair<int, int> >' is not derived from 'const std::move_iterator<_IteratorL>'
 1906 |                                 std::__lg(__last - __first) * 2,
      |                                           ~~~~~~~^~~~~~~~~