program noua;
var i,x:integer;
    s:longint;
function suma(n:longint):integer;
var s:integer;
begin
s:=0;
while n>0 do begin
s:=s+n mod 10;
n:=n div 10;
end;
suma:=s;
end;
begin
write('x=');
readln(x);
s:=0;
for i:=1 to x do s:=s+i;
writeln(suma(s));
readln;
end.