История изменений

(* program that sums integer values from A to B without loops
   2020 (c) saahriktu
   Under GNU GPLv3 *)
program sumatob;
uses sysutils;
var
   a, b, s : Int64;
begin
   if ParamCount < 2 then begin
      writeln('usage: sumatob A B');
      exit;
   end;
   if TryStrToInt64(ParamStr(1), a) = False then begin
      writeln('Error: invalid number A');
      exit;
   end;
   if TryStrToInt64(ParamStr(2), b) = False then begin
      writeln('Error: invalid number B');
      exit;
   end;
   if b < a then begin
      s := a;
      a := b;
      b := s;
   end;
   s := trunc((b - a + 1) * (a + b) / 2);
   writeln(s);
end.