var sum,n,i:integer;
begin
readln(n);
sum:=0;
for i:=1 to n do
sum:=sum+i;
writeln(sum);
readln;
end.
var sum,n,i:integer;
begin
readln(n);
sum:=0;
for i:=1 to n do
sum:=sum+i;
writeln(sum);
readln;
end.