Language: C++

#pragma GCC optimize "03"
#include "bits/stdc++.h"
using namespace std;
 
#define ll long long int
#define ld long double
#define pi pair<int, int>
#define pb push_back
#define fi first
#define se second
#define IOS ios::sync_with_stdio(false); cin.tie(0); cout.tie(0)
#ifndef LOCAL
#define endl '\n'
#endif
 
const int N = 1e5 + 5;
const int mod = 1e9 + 7;
const int inf = 1e9 + 9;
 
signed main() {
    IOS;
    #ifdef LOCAL
        freopen("input.txt","r", stdin);
        freopen("output.txt","w",stdout);
    #endif
    int a, b;
    cin >> a >> b;
    if((a+b)&1)
        cout << "IMPOSSIBLE";
    else
        cout << (a+b) >> 1;   
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:31:23: error: no match for 'operator>>' (operand types are 'std::basic_ostream<char>' and 'int')
   31 |         cout << (a+b) >> 1;
      |         ~~~~~~~~~~~~~ ^~ ~
      |              |           |
      |              |           int
      |              std::basic_ostream<char>
a.cc:31:23: note: candidate: 'operator>>(int, int)' (built-in)
   31 |         cout << (a+b) >> 1;
      |         ~~~~~~~~~~~~~~^~~~
a.cc:31:23: note:   no known conversion for argument 1 from 'std::basic_ostream<char>' to 'int'
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:41,
                 from a.cc:2:
/usr/include/c++/14/cstddef:131:5: note: candidate: 'template<class _IntegerType> constexpr std::__byte_op_t<_IntegerType> std::operator>>(byte, _IntegerType)'
  131 |     operator>>(byte __b, _IntegerType __shift) noexcept
      |     ^~~~~~~~
/usr/include/c++/14/cstddef:131:5: note:   template argument deduction/substitution failed:
a.cc:31:14: note:   cannot convert 'std::cout.std::basic_ostream<char>::operator<<((a + b))' (type 'std::basic_ostream<char>') to type 'std::byte'
   31 |         cout << (a+b) >> 1;
      |         ~~~~~^~~~~~~~
In file included from /usr/include/c++/14/string:55,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/basic_string.tcc:835:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
  835 |     operator>>(basic_istream<_CharT, _Traits>& __in,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.tcc:835:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/bitset:1597:5: note: candidate: 'template<class _CharT, class _Traits, long unsigned int _Nb> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, bitset<_Nb>&)'
 1597 |     operator>>(std::basic_istream<_CharT, _Traits>& __is, bitset<_Nb>& __x)
      |     ^~~~~~~~
/usr/include/c++/14/bitset:1597:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
In file included from /usr/include/c++/14/istream:1109,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/bits/istream.tcc:978:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _CharT&)'
  978 |     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c)
      |     ^~~~~~~~
/usr/include/c++/14/bits/istream.tcc:978:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/istream:849:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, unsigned char&)'
  849 |     operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
      |     ^~~~~~~~
/usr/include/c++/14/istream:849:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<char, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/istream:854:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, signed char&)'
  854 |     operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
      |     ^~~~~~~~
/usr/include/c++/14/istream:854:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<char, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/istream:896:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _CharT*)'
  896 |     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
      |     ^~~~~~~~
/usr/include/c++/14/istream:896:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/istream:939:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, unsigned char*)'
  939 |     operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/istream:939:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<char, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/istream:945:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, signed char*)'
  945 |     operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/istream:945:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<char, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/istream:1099:5: note: candidate: 'template<class _Istream, class _Tp> _Istream&& std::operator>>(_Istream&&, _Tp&&)'
 1099 |     operator>>(_Istream&& __is, _Tp&& __x)
      |     ^~~~~~~~
/usr/include/c++/14/istream:1099:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/istream: In substitution of 'template<class _Istream, class _Tp> _Istream&& std::operator>>(_Istream&&, _Tp&&) [with _Istream = std::basic_ostream<char>&; _Tp = int]':
a.cc:31:26:   required from here
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/istream:1099:5: error: no type named 'type' in 'struct std::enable_if<false, void>'
 1099 |     operator>>(_Istream&& __is, _Tp&& __x)
      |     ^~~~~~~~
/usr/include/c++/14/complex:509:5: note: candidate: 'template<class _Tp, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, complex<_Tp>&)'
  509 |     operator>>(basic_istream<_CharT, _Traits>& __is, complex<_Tp>& __x)
      |     ^~~~~~~~
/usr/include/c++/14/complex:509:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:143:
/usr/include/c++/14/iomanip:76:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _Resetiosflags)'
   76 |     operator>>(basic_istream<_CharT, _Traits>& __is, _Resetiosflags __f)
      |     ^~~~~~~~
/usr/include/c++/14/iomanip:76:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/iomanip:106:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _Setiosflags)'
  106 |     operator>>(basic_istream<_CharT, _Traits>& __is, _Setiosflags __f)
      |     ^~~~~~~~
/usr/include/c++/14/iomanip:106:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/iomanip:137:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _Setbase)'
  137 |     operator>>(basic_istream<_CharT, _Traits>& __is, _Setbase __f)
      |     ^~~~~~~~
/usr/include/c++/14/iomanip:137:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/iomanip:177:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _Setfill<_CharT>)'
  177 |     operator>>(basic_istream<_CharT, _Traits>& __is, _Setfill<_CharT> __f)
      |     ^~~~~~~~
/usr/include/c++/14/iomanip:177:5: note:   template argument deduction/substitution failed:
a.cc:31:26: note:   'std::basic_ostream<char>' is not derived from 'std::basic_istream<_CharT, _Traits>'
   31 |         cout << (a+b) >> 1;
      |                          ^
/usr/include/c++/14/iomanip:207:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _Setprecision)'
  207 |     operator>>(basic_istream<_CharT, _Traits>& __is, _Setprecision __f)
      |     ^~~~~~~~
/usr/include/c++/14/iomanip:207:5: note:   template argument deduction/substitution failed:
a.cc:31:26: n