Language: C++

// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC optimize("unroll-loops")

#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#ifdef on_linux
#include <sys/resource.h>
#endif

using namespace std;
using namespace __gnu_pbds;

#define sz(x)                   (int)((x).size())
#define all(x)                  (x).begin(), (x).end()
#define mem0(x)                 memset(x, 0, sizeof (x))
#define mem1(x)                 memset(x, -1, sizeof (x))
#define sleep(x)                std::this_thread::sleep_for(std::chrono::milliseconds(x))
#define DECIMAL(n)              std::cout << std::fixed << std::setprecision(n);
#define rep(i,a,b)              for(int32_t i = (a); i < (b); ++i)
#define between(i,x,y)          ((i) >= (x) && (i) <= (y))
// #define clamp(i,x,y)         clamp(i, x, y)
#define sqr(a)                  ((a) * (a))
#define pii                     pair<int32_t, int32_t>
#define pll                     pair<long long, long long>
#define mp                      make_pair
#define fi                      first
#define sc                      second
#define pb                      push_back
#define ppb                     pop_back
#define pf                      push_front
#define ppf                     pop_front
#define lbd                     lower_bound
#define ubd                     upper_bound
#define int                     long long
#define ll                      long long

template<typename T, typename U> istream& operator>>(istream& in, pair<T, U> &a) {in >> a.first >> a.second; return in;}
template<typename T, typename U> ostream& operator<<(ostream& out, pair<T, U> a) {out << "{" << a.first << ", " << a.second << "}"; return out;}
template<typename T, typename U> static inline void remin(T &x, U y) {if (y < x) {x = y;}}
template<typename T, typename U> static inline void remax(T &x, U y) {if (x < y) {x = y;}}

static mt19937_64 gen(chrono::duration_cast<chrono::nanoseconds>(chrono::high_resolution_clock::now().time_since_epoch()).count());

inline long long toint(const string &s) {stringstream ss; ss << s; long long x; ss >> x; return x;}
inline string tostring(long long number) {stringstream ss; ss << number; return ss.str();}
inline string tobin(long long x) {return bitset<63>(x).to_string();}

void alllower(string &u) {transform(u.begin(), u.end(), u.begin(), ::tolower); return;}
void allupper(string &u) {transform(u.begin(), u.end(), u.begin(), ::toupper); return;}

template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// find_by_order(k)  returns iterator to kth element starting from 0;
// order_of_key(k) returns count of elements strictly smaller than k;
// erase, insert same as normal set

const long double PI = 3.14159265358979323846264338;
const long double eps = 1e-12;
const long long fftmod = 998244353;
const long long MOD = 1e9 + 7;
const long long INF = 1e18;
const int32_t N = 1e5 + 10;
const int32_t NN = 1e6 + 10;



inline void dobbysolver(int testcase)
{
	int n;
	cin >> n;
	cout < n*(n + 1) / 2;




	return;
}

int32_t main()
{
#ifdef on_linux
	rlimit cpu_time {.rlim_cur = 2, .rlim_max = RLIM_INFINITY};
	setrlimit(RLIMIT_CPU, &cpu_time);
#endif
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	int TESTS = 1;
	//cin >> TESTS;
	for (int i = 1; i <= TESTS; ++i) {
		// cout << "Case #" << i << ": ";
		dobbysolver(i);
		if (i != TESTS)	cout << '\n';
	}
	return 0;
}

Compiler output:
a.cc: In function 'void dobbysolver(long long int)':
a.cc:75:14: error: no match for 'operator<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'long long int')
   75 |         cout < n*(n + 1) / 2;
      |         ~~~~ ^ ~~~~~~~~~~~~~
      |         |                |
      |         |                long long int
      |         std::ostream {aka std::basic_ostream<char>}
a.cc:75:14: note: candidate: 'operator<(int, long long int)' (built-in)
   75 |         cout < n*(n + 1) / 2;
      |         ~~~~~^~~~~~~~~~~~~~~
a.cc:75:14: note:   no known conversion for argument 1 from 'std::ostream' {aka 'std::basic_ostream<char>'} to 'int'
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:7:
/usr/include/c++/14/bits/regex.h:1143:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1143 |     operator<(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1143:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/regex.h:1224:5: 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>&)'
 1224 |     operator<(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1224:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/regex.h:1317:5: 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>&)'
 1317 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1317:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/regex.h:1391:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1391 |     operator<(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1391:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'long long int'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/regex.h:1485:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1485 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1485:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/regex.h:1560:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1560 |     operator<(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1560:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'long long int'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/regex.h:1660:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1660 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1660:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
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:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::pair<_T1, _T2>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
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/c++/14/string_view:673:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  673 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:673:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/string_view:680:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  680 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:680:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/string_view:688:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  688 |     operator< (__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:688:5: note:   template argument deduction/substitution failed:
a.cc:75:28: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'long long int'
   75 |         cout < n*(n + 1) / 2;
      |                            ^
/usr/include/c++/14/bits/basic_string.h:3874:5: note: candidate: 'template<class _Cha