[@Rafa3L]

Код:

const
 n = 30;
 A = 5;
var
 i, sm: integer;
 X: array[1..n] of integer;
begin
 for i := Low(X) to High(X) do X[i]:= i;
 sm:= 0;
 if A < n then
  for i := A+1 to High(X) do Inc(sm, X[i])
 else sm:= 10;
 ShowMessage('Ответ: ' + IntToStr(sm));
end;