program d;
uses crt;
var
s, k, n, i: integer;
begin
clrscr;
readln(k);
readln(n);
i := k
while i < (k+n) do
begin
Inc(s, i);
Inc(i);
end;
Writeln (s);
readkey;
end.
program d;
uses crt;
var
s, k, n, i: integer;
begin
clrscr;
readln(k);
readln(n);
i := k
while i < (k+n) do
begin
Inc(s, i);
Inc(i);
end;
Writeln (s);
readkey;
end.