Language: C++

/*
 *  AUTHOR : MANAV PATEl
*/
#include<bits/stdc++.h>
#include<functional>
//#include<boost/multiprecision/cpp_int.hpp>
//using namespace boost::multiprecision;
using namespace std;

namespace fastio {

	template <class T> istream &operator>>(istream &os, vector<T> & vec) {
		for (auto &u : vec)os >> u;
		return os;
	}
	template <class T> ostream &operator<<(ostream &os, const vector<T> & vec) {
		for (auto &u : vec)os << u << " ";
		return os;
	}
	template<class T1, class T2> inline istream& operator>>(istream& os, pair<T1, T2>& p) {
		return os >> p.first >> p.second;
	}
	template<class T1, class T2> ostream& operator<<(ostream& os, const pair<T1, T2>& p) {
		return os << p.first << " " << p.second;
	}
	template <class T> ostream &operator<<(ostream &os, set<T> & con) {
		for (auto &u : con) os << u << " ";
		return os;
	}
	void re() {}
	template <typename T, typename... args> void re(T& x, args&... tail) {
		cin >> x;
		re(tail...);
	}
	void pr() {}
	template <typename T> void pr(const T& x) {
		cout << x;
	}
	template <typename T, typename... args> void pr(const T& x, const args&... tail) {
		cout << x << " ";
		pr(tail...);
	}
	template <typename... args> void prln(const args&... tail) {
		pr(tail...);
		cout << "\n";
	}
}
using namespace fastio;

typedef long long int ll;
typedef long double ld;

const ll mod = 1e9+7;
const ll mod1 = 998244353;

#define fill(a)  memset(a, 0, sizeof(a))
#define fst first
#define snd second
#define mp make_pair
#define pb push_back

int main()
{
	cin.sync_with_stdio(false);
	cin.exceptions(cin.failbit);
	cin.tie(0);
	ll a, b;
	re(a,b);
	if((a+b)% 2==  0)
	{
		cout << (a+b)/2 <"\n";
	}
	else cout << "IMPOSSIBLE\n";
}



Compiler output:
a.cc: In function 'int main()':
a.cc:71:33: error: no match for 'operator<' (operand types are 'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} and 'const char [2]')
   71 |                 cout << (a+b)/2 <"\n";
      |                 ~~~~~~~~~~~~~~~ ^~~~~
      |                      |           |
      |                      |           const char [2]
      |                      std::basic_ostream<char>::__ostream_type {aka std::basic_ostream<char>}
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:4:
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'const char [2]'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'const char [2]'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::pair<_T1, _T2>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>::__ostream_type' {aka 'std::basic_ostream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
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:71:34: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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:71:34: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   71 |                 cout << (a+b)/2 <"\n";
      |                                  ^~~~
/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,
      |     ^~~~~~~~
/