var
a, b, kol, i: longint;
begin
readln(a, b);
if a <= b then
for i := a to b do
inc(kol, i)
else
for i := a downto b do
inc(kol, i);
writeln(kol);
end.
var
a, b, kol, i, q: longint;
begin
readln(a, b);
if a > b then
begin
q := b;
b := a;
a := q;
end;
for i := a to b do
inc(kol, i);
writeln(kol);
end.