Simple conceptions in Pascal

//fpc 3.0.0

program HelloWorld;

function f(x: Integer): Integer;
begin
    f := x * 2;
end;


var abc, bcd: Integer;
begin
    abc := 10;
    readln(bcd);
    writeln('Hello, world!');
    writeln('result is: ', f(abc + bcd));
end.