Language: C++

#include <iostream>
int main(){
  int n,m;
  bool b1[n+10];
  bool b2[n+10];
  cin >> n >> m;
  for(int i=0; i<m; i++){
    int a,b;
    cin >> a >> b;
    if(a>b) swap(a,b);
    if(a==1) b1[b]=true;
    if(b==n) b2[a]=true;
  }
  for(int i=1; i<=m; i++){
    if(b1[i]==true && b2[i]==true){
      cout << "POSSIBLE" << endl;
    }
    return 0;
  }
  cout << "IMPOSSIBLE" << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |   cin >> n >> m;
      |   ^~~
      |   std::cin
In file included from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:10:13: error: 'swap' was not declared in this scope
   10 |     if(a>b) swap(a,b);
      |             ^~~~
a.cc:10:13: note: suggested alternatives:
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/string:68,
                 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:
/usr/include/c++/14/tuple:2823:5: note:   'std::swap'
 2823 |     swap(tuple<_Elements...>&, tuple<_Elements...>&) = delete;
      |     ^~~~
In file included from /usr/include/c++/14/bits/exception_ptr.h:41,
                 from /usr/include/c++/14/exception:166,
                 from /usr/include/c++/14/ios:41:
/usr/include/c++/14/bits/move.h:226:5: note:   'std::swap'
  226 |     swap(_Tp& __a, _Tp& __b)
      |     ^~~~
/usr/include/c++/14/bits/move.h:226:5: note:   'std::swap'
/usr/include/c++/14/bits/exception_ptr.h:229:5: note:   'std::__exception_ptr::swap'
  229 |     swap(exception_ptr& __lhs, exception_ptr& __rhs)
      |     ^~~~
a.cc:16:7: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   16 |       cout << "POSSIBLE" << endl;
      |       ^~~~
      |       std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:16:29: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   16 |       cout << "POSSIBLE" << endl;
      |                             ^~~~
      |                             std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:20:3: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   20 |   cout << "IMPOSSIBLE" << endl;
      |   ^~~~
      |   std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:20:27: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   20 |   cout << "IMPOSSIBLE" << endl;
      |                           ^~~~
      |                           std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~