var
b, i, sum : integer;
begin
readln (b);
sum:= 0;
for i:= 0 to b do
sum:=sum+i;
writeln (sum);
end.
var
b, i, sum : integer;
begin
readln (b);
sum:= 0;
for i:= 0 to b do
sum:=sum+i;
writeln (sum);
end.