{programmer:mogtaba amirzade 
url http:\\www.ifjam.com
}
program p3(input,output); {12}
var
x,s,i,n:integer;
begin
s:=0;
i:=1;
readln(n);
while i<=n do
begin
s:=s+i;
i:=i+1;
end;
writeln(s:10);
readln
end.