Language: C++

#include "bits/stdc++.h"

#define REP(i,n) for(ll i=0;i<ll(n);++i)
#define RREP(i,n) for(ll i=ll(n)-1;i>=0;--i)
#define FOR(i,m,n) for(ll i=m;i<ll(n);++i)
#define RFOR(i,m,n) for(ll i=ll(n)-1;i>=ll(m);--i)
#define ALL(v) (v).begin(),(v).end()
#define UNIQUE(v) v.erase(unique(ALL(v)),v.end());
#define INF 1000000001ll
#define MOD 1000000007ll
#define EPS 1e-9

const int dx[8] = { 1,1,0,-1,-1,-1,0,1 };
const int dy[8] = { 0,1,1,1,0,-1,-1,-1 };


using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;



int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int h, w;
	cin >> h >> w;
	vector<set<int>> st(h + 1);
	int n;
	cin >> n;
	REP(i, n) {
		int a, b;
		cin >> a >> b;
		a--; b--;
		st[a].insert(b);
	}
	REP(i, w)st[h].insert(i);
	int m = 0;
	REP(i, h) {

		if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
			cout << i + 1 << endl;
			return 0;
		}

		if (st[i + 1].count(m + 1) == 0)m++;
	}
}


Compiler output:
a.cc: In function 'int main()':
a.cc:46:61: error: no match for 'operator<=' (operand types are 'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} and 'int')
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                           ~~~~~~~~~~~~~~~~~ ^~ ~
      |                                                          |     |
      |                                                          |     int
      |                                                          std::set<int>::iterator {aka std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator}
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1154:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator<=(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1154 |     operator<=(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1154:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/regex.h:1260:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator<=(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1260 |     operator<=(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1260:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/regex.h:1353:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator<=(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1353 |     operator<=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1353:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/regex.h:1427:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<=(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1427 |     operator<=(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1427:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/regex.h:1521:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1521 |     operator<=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1521:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/regex.h:1599:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<=(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1599 |     operator<=(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1599:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/regex.h:1699:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1699 |     operator<=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1699:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1064:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1064 |     operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1064:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::pair<_T1, _T2>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:469:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  469 |     operator<=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:469:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::reverse_iterator<_Iterator>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/stl_iterator.h:513:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  513 |     operator<=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:513:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::reverse_iterator<_Iterator>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/stl_iterator.h:1704:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1704 |     operator<=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1704:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::move_iterator<_IteratorL>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
/usr/include/c++/14/bits/stl_iterator.h:1767:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1767 |     operator<=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1767:5: note:   template argument deduction/substitution failed:
a.cc:46:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::move_iterator<_IteratorL>'
   46 |                 if (!st[i + 1].empty() && st[i + 1].begin() <= m) {
      |                                                                ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/