Language: C++

#include<bits/stdc++.h>
using namespace;
int main()
{
    int N; cin >> N;
    string S; cin >> S;
    int ans = 0;
    for(int i = 1; i < N; i++)
    {
        int cnt = 0;
        for(char c = 'a'; c <= 'z'; c++)
        {
            bool left = false,right = false;
            for(int j = 0; j < i; j++) //左側の判定
            {
                if(S.at(j) == c)
                {
                    left = True;
                }
            }
            for(int j = i; j < N; j++) //右側の判定
            {
                if(S.at(j) == c)
                {
                    right = True;
                }
            }
            if(left && right)
            {
                cnt++;
            }
        }
        if(ans < cnt)
        {
            ans = cnt;
        }
    }
    cout << ans << endl;
}

Compiler output:
a.cc:2:16: error: expected identifier before ';' token
    2 | using namespace;
      |                ^
a.cc: In function 'int main()':
a.cc:5:12: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    5 |     int N; cin >> N;
      |            ^~~
      |            std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146,
                 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:6:5: error: 'string' was not declared in this scope
    6 |     string S; cin >> S;
      |     ^~~~~~
a.cc:6:5: note: suggested alternatives:
In file included from /usr/include/c++/14/string:41,
                 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/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:6:22: error: 'S' was not declared in this scope
    6 |     string S; cin >> S;
      |                      ^
a.cc:18:28: error: 'True' was not declared in this scope
   18 |                     left = True;
      |                            ^~~~
a.cc:25:29: error: 'True' was not declared in this scope
   25 |                     right = True;
      |                             ^~~~
a.cc:38:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   38 |     cout << ans << 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:38:20: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   38 |     cout << ans << endl;
      |                    ^~~~
      |                    std::endl
In file included from /usr/include/c++/14/istream:41,
                 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/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~