var fv,fr:text;
i,vt,a,b,d,s:int64;
begin
assign(fv,'math.inp'); reset(fv);
assign(fr,'math.out'); rewrite(fr);
read(fv,a,b);
i:=0; d:=1;
while a>i do
begin
i:=i+d; d:=d+1; end; vt:=a;
repeat
if b<=i then s:=s+(d-1)*(b-vt+1) else s:=s+(d-1)*(i-vt+1);
vt:=i+1; i:=i+d; d:=d+1;
until b<i;
write(fr,s); close(fv); close(fr);
end.