def main(io)
  n = io.get
  p = Array.new(n, 0)

  io.put_e 0 if n == 1

  (0...n//2).each do |i|
    if i.even?
      p[i] = i+1
      p[-1-i] = n-i
    else
      p[i] = n-i
      p[-1-i] = i+1
    end
  end
  p[n//2] = n//2+1 if n.odd?

  r = n.to_i64
  p.each_cons_pair do |i, j|
    r += i.to_i64*j
  end
  io.put r
end

class ProconIO
  def initialize
    @buf = [] of String
    @index = 0
  end

  def get(k : T.class = Int32) forall T
    get_v(k)
  end

  def get(*ks : T.class) forall T
    ks.map { |k| get_v(k) }
  end

  macro define_getn
    {% for i in (2..9) %}
      def get{{i}}(k : T.class = Int32) forall T
        get({% for j in (1..i) %}k{% if j < i %}, {% end %}{% end %})
      end
    {% end %}
  end
  define_getn

  def get_a(n : Int, k : T.class = Int32) forall T
    Array.new(n) { get_v(k) }
  end

  def get_c(n : Int, k : T.class = Int32) forall T
    get_a(n, k)
  end

  def get_c(n : Int, *ks : T.class) forall T
    a = Array.new(n) { get(*ks) }
    ks.map_with_index { |_, i| a.map { |e| e[i] } }
  end

  macro define_getn_c
    {% for i in (2..9) %}
      def get{{i}}_c(n : Int, k : T.class = Int32) forall T
        get_c(n, {% for j in (1..i) %}k{% if j < i %}, {% end %}{% end %})
      end
    {% end %}
  end
  define_getn_c

  def get_m(r : Int, c : Int, k : T.class = Int32) forall T
    Array.new(r) { get_a(c, k) }
  end

  def put(*vs)
    vs.each.with_index do |v, i|
      put_v(v)
      print i < vs.size - 1 ? " " : "\n"
    end
  end

  def put_e(*vs)
    put(*vs)
    exit
  end


  private def get_v(k : Int32.class); get_token.to_i32; end
  private def get_v(k : Int64.class); get_token.to_i64; end
  private def get_v(k : String.class); get_token; end

  private def get_token
    if @buf.size == @index
      @buf = read_line.split
      @index = 0
    end
    v = @buf[@index]
    @index += 1
    v
  end

  private def put_v(vs : Enumerable)
    vs.each_with_index do |v, i|
      print v
      print " " if i < vs.size - 1
    end
  end

  private def put_v(v)
    print v
  end
end

main(ProconIO.new)