program Laba2_2;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type
   TArr = array of Integer;

const
   OutputFileName = 'output.txt';
   INputFileName= 'input.txt';

var
   Range: Integer;

function IsCorrectInput(var Number: Integer; const Min, Max: Integer): Integer;
var
   IsCorrect: boolean;
begin
   IsCorrect := False;
   repeat
      try
         Readln(Number);
         if (Number < Min) or (Max < Number) then
            Writeln('The number must be between ', Min, ' and ', Max, '!')
         else
            IsCorrect:= True;
      except
         Write('Error! Enter a number: ');
      end;
   until IsCorrect;
   Result := Number;
end;

procedure FindFriendshipNumbers(var Range: integer; var Numbers: TArr);
var
   del:array of integer;
   i, j, k, p: integer;
begin
   SetLength(del, Range);
   for k := 2 to Range do
      del[k] := 1 + k;
    for k := 2 to Range div 2 do
    begin
       p := k + k;
       while p < Range + 1 do
       begin
          del[p] := del[p] + k;
          p:= p + k;
       end;
    end;
     for i := 2 to Range - 1 do
        for j := i + 1 to Range do
            if (del[i] = i + j) and (del[j] = i + j)then
            begin
               SetLength(Numbers, Length(Numbers) + 2);
               Numbers[High(Numbers) - 1] := i;
               Numbers[High(Numbers)] := j;
            end;
end;

procedure OutputConsole(const Numbers: TArr);
var
   i: Integer;
begin
   i := 0;
   while i < Length(Numbers) do
   begin
      Writeln(Numbers[i],' | ', Numbers[i + 1]);
      Inc(i, 2);
   end;
end;

procedure OutputFile(const Numbers: TArr);
var
   UserFile: TextFile;
   i: Integer;
begin
   AssignFile(UserFile, OutputFileName);
   Rewrite(UserFile);
   i := 0;
   while i < Length(NUmbers) do
   begin
      Writeln(UserFile, Numbers[i], ' | ', Numbers[i + 1]);
      Inc(i, 2);
   end;
   CloseFile(UserFile);
end;

procedure InputFile(var Range: Integer);
var
   UserFile: TextFile;
begin
   AssignFile(UserFile, InputFileName);
   Reset(UserFile);
   Read(UserFile, Range);
   CloseFile(UserFile);
end;

function GetUserChoice: Char;
var
   Choice: Char;
begin
   Writeln('Do you want to read from file?[Y/N]');
   Readln(Choice);
   GetUserChoice := Choice;
end;

procedure Main();
var
   Numbers: TArr;
   Answer: Char;
begin
   Writeln('This program finds pairs of friendly numbers.');
   //Write('Enter the top of the friendly number range: ');
   Answer := getUserChoice;
   if Answer = 'Y' then
   begin
      InputFile(Range);
      Writeln(Range);
   end
   else
   begin
      Writeln('Enter the upper limit of the friendly number search range.');
      Writeln('The number must be up to 10.000 !');
      IsCorrectInput(Range, 2, 10000);
   end;
   FindFriendshipNumbers(Range, Numbers);
   OutputConsole(Numbers);
   OutputFile(Numbers);
   Readln;
end;

begin
   Main
end.