def solve(io)
  n = io.get(Int64)
  io.put n*3//2
end

class Array
  macro new_md(*args, &block)
    {% if !block %}
      {% for arg, i in args[0...-2] %}
        Array.new({{arg}}) {
      {% end %}
      Array.new({{args[-2]}}, {{args[-1]}})
      {% for arg in args[0...-2] %}
        }
      {% end %}
    {% else %}
      {% for arg, i in args %}
        Array.new({{arg}}) { |_i{{i}}|
      {% end %}
      {% for block_arg, i in block.args %}
        {{block_arg}} = _i{{i}}
      {% end %}
      {{block.body}}
      {% for arg in args %}
        }
      {% end %}
    {% end %}
  end
end
struct Int
  def cdiv(b : Int)
    (self + b - 1) // b
  end

  {% if compare_versions(env("CRYSTAL_VERSION") || "0.0.0", "0.34.0") < 0 %}
    def bit_length : Int32
      x = self < 0 ? ~self : self

      if x.is_a?(Int::Primitive)
        Int32.new(sizeof(self) * 8 - x.leading_zeros_count)
      else
        to_s(2).size
      end
    end
  {% end %}
end

struct Int32
  SQRT_MAX = 46_340_i32

  def isqrt
    m = SQRT_MAX
    r = (1_i32..SQRT_MAX).bsearch { |i| i**2 > self }
    r.nil? ? SQRT_MAX : r - 1
  end
end

struct Int64
  SQRT_MAX = 3_037_000_499_i64

  def isqrt
    r = (1_i64..SQRT_MAX).bsearch { |i| i**2 > self }
    r.nil? ? SQRT_MAX : r - 1
  end
end
struct Number
  {% if compare_versions(env("CRYSTAL_VERSION") || "0.0.0", "0.36.0") < 0 %}
    def self.additive_identity
      zero
    end

    def self.multiplicative_identity
      new(1)
    end
  {% end %}
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

macro min_u(a, b)
  {{a}} = Math.min({{a}}, {{b}})
end

macro max_u(a, b)
  {{a}} = Math.max({{a}}, {{b}})
end

solve(ProconIO.new)