Language: C++

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args) {
        int n = int.Parse(Console.ReadLine());
        List<int> a = Console.ReadLine().Split().Select(int.Parse).ToList();
        Console.WriteLine(solve(n, a));
    }
    static int solve(int n, List<int> a) {
        int[] lgcd = new int[n-1];
        lgcd[0] = a[0];
        for(int i = 1; i < n-1; i ++) {
            lgcd[i] = Gcd(a[i],lgcd[i-1]);
        }
        a.Reverse();
        int[] rgcd = new int[n-1];
        rgcd[0] = a[0];
        for(int i = 1; i < n-1; i ++) {
            rgcd[i] = Gcd(a[i],rgcd[i-1]);
        }
        a.Reverse();
        int[] ans = new int[n];
        ans[0] = rgcd[n-2];
        ans[n-1] = lgcd[n-2];
        for(int i = 1; i < n-1; i ++) {
            ans[i] = Gcd(lgcd[i-1], rgcd[n-2-i]);
        }
        return ans.Max();
    }
    static int Gcd(int a, int b) {
        if (a < b) return Gcd(b, a);
        while (b != 0) {
            var tmp = a % b;
            a = b;
            b = tmp;
        }
        return a;
    }
}

Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Linq;
      |       ^~~~~~
a.cc:7:22: error: 'string' has not been declared
    7 |     static void Main(string[] args) {
      |                      ^~~~~~
a.cc:7:31: error: expected ',' or '...' before 'args'
    7 |     static void Main(string[] args) {
      |                               ^~~~
a.cc:12:29: error: 'List' has not been declared
   12 |     static int solve(int n, List<int> a) {
      |                             ^~~~
a.cc:12:33: error: expected ',' or '...' before '<' token
   12 |     static int solve(int n, List<int> a) {
      |                                 ^
a.cc:42:2: error: expected ';' after class definition
   42 | }
      |  ^
      |  ;
a.cc: In static member function 'static void Program::Main(int*)':
a.cc:8:17: error: expected primary-expression before 'int'
    8 |         int n = int.Parse(Console.ReadLine());
      |                 ^~~
a.cc:9:9: error: 'List' was not declared in this scope
    9 |         List<int> a = Console.ReadLine().Split().Select(int.Parse).ToList();
      |         ^~~~
a.cc:9:14: error: expected primary-expression before 'int'
    9 |         List<int> a = Console.ReadLine().Split().Select(int.Parse).ToList();
      |              ^~~
a.cc:10:9: error: 'Console' was not declared in this scope
   10 |         Console.WriteLine(solve(n, a));
      |         ^~~~~~~
a.cc:10:36: error: 'a' was not declared in this scope
   10 |         Console.WriteLine(solve(n, a));
      |                                    ^
a.cc: In static member function 'static int Program::solve(int, int)':
a.cc:13:12: error: structured binding declaration cannot have type 'int'
   13 |         int[] lgcd = new int[n-1];
      |            ^~
a.cc:13:12: note: type must be cv-qualified 'auto' or reference to cv-qualified 'auto'
a.cc:13:12: error: empty structured binding declaration
a.cc:13:15: error: expected initializer before 'lgcd'
   13 |         int[] lgcd = new int[n-1];
      |               ^~~~
a.cc:14:9: error: 'lgcd' was not declared in this scope
   14 |         lgcd[0] = a[0];
      |         ^~~~
a.cc:14:19: error: 'a' was not declared in this scope
   14 |         lgcd[0] = a[0];
      |                   ^
a.cc:19:12: error: structured binding declaration cannot have type 'int'
   19 |         int[] rgcd = new int[n-1];
      |            ^~
a.cc:19:12: note: type must be cv-qualified 'auto' or reference to cv-qualified 'auto'
a.cc:19:12: error: empty structured binding declaration
a.cc:19:15: error: expected initializer before 'rgcd'
   19 |         int[] rgcd = new int[n-1];
      |               ^~~~
a.cc:20:9: error: 'rgcd' was not declared in this scope
   20 |         rgcd[0] = a[0];
      |         ^~~~
a.cc:25:12: error: structured binding declaration cannot have type 'int'
   25 |         int[] ans = new int[n];
      |            ^~
a.cc:25:12: note: type must be cv-qualified 'auto' or reference to cv-qualified 'auto'
a.cc:25:12: error: empty structured binding declaration
a.cc:25:15: error: expected initializer before 'ans'
   25 |         int[] ans = new int[n];
      |               ^~~
a.cc:26:9: error: 'ans' was not declared in this scope
   26 |         ans[0] = rgcd[n-2];
      |         ^~~
a.cc: In static member function 'static int Program::Gcd(int, int)':
a.cc:36:13: error: 'var' was not declared in this scope
   36 |             var tmp = a % b;
      |             ^~~
a.cc:38:17: error: 'tmp' was not declared in this scope
   38 |             b = tmp;
      |                 ^~~