/TITO - Tính tổng (OLPCĐ 2014)

              USES CRT;
        var     r1,r2:real;
                temp1,temp2,ssh,t:int64;
                begin
                    readln(r1,r2);
                    if (trunc(r1)<>r1) then temp1:=trunc(r1)+1 else
                    temp1:=trunc(r1);
                    temp2:=trunc(r2);
                    ssh:=temp2-temp1+1;
                    t:=(temp2+temp1)*ssh div 2;
                    writeln(t);
                end.