program var_27_task_3;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

var
    Pi : Real;
    Precision, K : Integer;
    I : Integer = 0;
    Numerator : Integer = 1;
    FirstDenominator : Integer = 1;
    SecondDenominator : Integer = 3;
    Counter : Integer = 1;

begin
    Precision := 0;
    While Precision <= 0 do
    begin
        try
            WriteLn('Enter precision (number of iterations) : ');
            ReadLn(Precision);
        except
        on E: Exception do
            Writeln(E.ClassName, ': ', E.Message);
    end;

    if Precision<=0 then
        begin
            WriteLn('Input Error. Check if the data is correct.');
        end;
    end;

    While I < (Precision*3) do
    begin
        if Counter < 3 then
            begin
                Pi := Pi + Numerator/(FirstDenominator*SecondDenominator);
            end
        else if Counter = 3 then
            begin
                Pi := Pi - Numerator/(FirstDenominator*SecondDenominator);
            end;

        FirstDenominator := FirstDenominator + 4;
        SecondDenominator := SecondDenominator + 4;
        Counter := Counter + 1;
        if Counter > 3 then
            begin
                Counter := 1;
            end;
        I := I + 1;
    end;


    WriteLn('Pi value = ', Pi*8);
    Writeln('Press <enter> to quit...');
    Readln;
end.