bằng pascal?
var dau , cuoi ,result: integer;
begin
writeln('nhap so dau');
readln(dau);
writeln('nhap so cuoi');
readln(cuoi);
if (dau > 500 and cuoi > dau ) then
result = (dau + cuoi) * ((cuoi +1 )/2);
writeln('ket qua' + result);
esle
writeln('dau phai > 500');
readln
end.