const SIZE = 10000; LEN...

const
  SIZE = 10000;
  LENGTH = 10;
var
  sum : longint;
  n, m, i, j : integer;
  a : array[1..SIZE, 1..LENGTH] of integer;
function h(u, v : integer) : integer;
var
  ans, i : integer;
begin
  ans := 0;
  for i := 1 to n do
    if a[u][i] <> a[v][i] then
      inc(ans);
  h := ans;
end;
begin
  readln(n);
  fillchar(a, sizeof(a), 0);
  m := 1;
  repeat
    i := 1;
    while (i <= n) and (a[m][i] = 1) do
      inc(i);
    if i > n then
      break;
    inc(m);
    a[m][i] := 1;
    for j := i + 1 to n do
      a[m][j] := a[m - 1][j];
  until false;
  sum := 0;
  for i := 1 to m do
    for j := 1 to m do
      sum := sum + h(i, j);
  writeln(sum);
end.