program baitap;
var n:integer;
tong:longint;
const fi='bai2.inp';
fo='bai3.out';
procedure nhap;
var f:text;
begin
assign(f,fi);
reset(f);
readln(f,n);
close(f);
end;
procedure xuli;
var i:integer;
begin
tong:=0;
for i:=1 to n do tong:=tong+i;
end;
procedure xuat;
var f:text;
begin
assign(f,fo);
rewrite(f);
writeln(f,tong);
close(f);
end;
begin
nhap;
xuli;
xuat;
end.