Language: C++

using System;
using System.Collections.Generic;
using System.Linq;
class Ho{
  static void Main(){
    var k = int.Parse(Console.ReadLine());
    var zen = new double[k,2];
   
    for(var i = 0;i<k;i++){
       var aho = Console.ReadLine().Split();
       zen[i,0] = double.Parse(aho[0]);
       zen[i,1] = double.Parse(aho[1]);
    }
    double go  = 0;
    for(var i = 0;i<k;i++){
    	for(var j = 0;j<k;j++){
          if(i == j) continue;
           double x = (zen[i,0]-zen[j,0]);
           double y = (zen[i,1]-zen[j,1]);
           double kyori = Math.Sqrt(x*x+y*y);
           go += kyori;
        }
    }
    Console.WriteLine(go/k);
  }
}

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:26:2: error: expected ';' after class definition
   26 | }
      |  ^
      |  ;
a.cc: In static member function 'static void Ho::Main()':
a.cc:6:5: error: 'var' was not declared in this scope
    6 |     var k = int.Parse(Console.ReadLine());
      |     ^~~
a.cc:7:9: error: expected ';' before 'zen'
    7 |     var zen = new double[k,2];
      |         ^~~
a.cc:9:13: error: expected ';' before 'i'
    9 |     for(var i = 0;i<k;i++){
      |             ^
a.cc:9:19: error: 'i' was not declared in this scope
    9 |     for(var i = 0;i<k;i++){
      |                   ^
a.cc:9:21: error: 'k' was not declared in this scope
    9 |     for(var i = 0;i<k;i++){
      |                     ^
a.cc:10:12: error: expected ';' before 'aho'
   10 |        var aho = Console.ReadLine().Split();
      |            ^~~
a.cc:11:8: error: 'zen' was not declared in this scope
   11 |        zen[i,0] = double.Parse(aho[0]);
      |        ^~~
a.cc:11:19: error: expected primary-expression before 'double'
   11 |        zen[i,0] = double.Parse(aho[0]);
      |                   ^~~~~~
a.cc:12:19: error: expected primary-expression before 'double'
   12 |        zen[i,1] = double.Parse(aho[1]);
      |                   ^~~~~~
a.cc:15:13: error: expected ';' before 'i'
   15 |     for(var i = 0;i<k;i++){
      |             ^
a.cc:15:19: error: 'i' was not declared in this scope
   15 |     for(var i = 0;i<k;i++){
      |                   ^
a.cc:15:21: error: 'k' was not declared in this scope
   15 |     for(var i = 0;i<k;i++){
      |                     ^
a.cc:16:17: error: expected ';' before 'j'
   16 |         for(var j = 0;j<k;j++){
      |                 ^
a.cc:16:23: error: 'j' was not declared in this scope
   16 |         for(var j = 0;j<k;j++){
      |                       ^
a.cc:18:24: error: 'zen' was not declared in this scope
   18 |            double x = (zen[i,0]-zen[j,0]);
      |                        ^~~
a.cc:20:27: error: 'Math' was not declared in this scope
   20 |            double kyori = Math.Sqrt(x*x+y*y);
      |                           ^~~~
a.cc:24:5: error: 'Console' was not declared in this scope
   24 |     Console.WriteLine(go/k);
      |     ^~~~~~~
a.cc:24:26: error: 'k' was not declared in this scope
   24 |     Console.WriteLine(go/k);
      |                          ^