def solve(io) n = io.get g = Graph.new(n) (n-1).times do |i| ai = io.get g.add_edge_b(i+1, ai) end t = g.tree(0) e = t.euler_tour f = FenwickTree(Int32).new(e.path.size) r = 0_i64 (0...n).reverse_each do |u| r += f[e.in_time[u]..e.out_time[u]] f.add(e.in_time[u], 1) end io.put r end struct Int def cdiv(b : Int) (self + b - 1) // b end def bit?(i : Int) bit(i) == 1 end def set_bit(i : Int) self | (self.class.new(1) << i) end def reset_bit(i : Int) self & ~(self.class.new(1) << i) 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 Float64 def near_zero? self.abs < EPSILON end end struct Number {% if compare_versions(env("CRYSTAL_VERSION") || "0.0.0", "1.1.0") < 0 %} def zero? self == 0 end def positive? self > 0 end def negative? self < 0 end {% end %} {% 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 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 class ProconIO def initialize(@ins : IO = STDIN, @outs : IO = STDOUT) @buf = IO::Memory.new("") end def get(k : T.class = Int32) forall T get_v(k) end macro define_get {% for i in (2..9) %} def get({{ *(1..i).map { |j| "k#{j}".id } }}) { {{ *(1..i).map { |j| "get(k#{j})".id } }} } end {% end %} end define_get macro define_getn {% for i in (2..9) %} def get{{i}}(k : T.class = Int32) forall T get({{ *(1..i).map { "k".id } }}) 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 macro define_get_c {% for i in (2..9) %} def get_c(n : Int, {{ *(1..i).map { |j| "k#{j}".id } }}) a = Array.new(n) { get({{ *(1..i).map { |j| "k#{j}".id } }}) } { {{ *(1..i).map { |j| "a.map { |e| e[#{j-1}] }".id } }} } end {% end %} end define_get_c macro define_getn_c {% for i in (2..9) %} def get{{i}}_c(n : Int, k : T.class = Int32) forall T get_c(n, {{ *(1..i).map { "k".id } }}) 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 macro define_put {% for i in (1..9) %} def put({{ *(1..i).map { |j| "v#{j}".id } }}, *, delimiter = " ") {% for j in (1..i) %} print_v(v{{j}}, delimiter) {% if j < i %}@outs << delimiter{% end %} {% end %} @outs.puts end {% end %} end define_put def put_e(*vs) put(*vs) exit end def put_f(*vs) put(*vs) @outs.flush 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 : UInt32.class); get_token.to_u32; end private def get_v(k : UInt64.class); get_token.to_u64; end private def get_v(k : Float64.class); get_token.to_f64; end private def get_v(k : String.class); get_token; end private def get_token loop do token = @buf.gets(' ', chomp: true) break token unless token.nil? @buf = IO::Memory.new(@ins.read_line) end end private def print_v(v, dlimiter) @outs << v end private def print_v(v : Enumerable, delimiter) v.each_with_index do |e, i| @outs << e @outs << delimiter if i < v.size - 1 end end end macro min_u(a, b) {{a}} = Math.min({{a}}, {{b}}) end macro max_u(a, b) {{a}} = Math.max({{a}}, {{b}}) end macro zip(a, *b, &block) {{a}}.zip({{*b}}) {{block}} end class FenwickTree(T) def initialize(@n : Int32) @b = Array.new(@n + 1, T.additive_identity) end def [](i : Int) self[i..i] end def [](start : Int, count : Int) get(start + count) - get(start) end def [](r : Range) sc = Indexable.range_to_index_and_count(r, @n) raise ArgumentError.new("Invalid range") if sc.nil? self[*sc] end def add(i : Int, val : T) i += 1 while i <= @n @b[i] += val i += i & -i end end @b : Array(T) private def get(i : Int) s = T.additive_identity while i > 0 s += @b[i] i -= i & -i end s end end require "bit_array" class Graph alias Node = Int32 def initialize(@size : Node) @g = Array(Array(Node)).new(@size) { [] of Node } end getter size : Int32 delegate :[], to: @g def add_edge(u : Node, v : Node) @g[u] << v end def add_edge_b(u : Node, v : Node) @g[u] << v @g[v] << u end def bfs(u : Node) b = BitArray.new(@size) yield u, -1 b[u] = true q = Deque.new([u]) until q.empty? v = q.shift @g[v].each do |w| next if b[w] yield w, v b[w] = true q.push(w) end end end end class GraphW(T) alias Node = Int32 struct Edge(T) def initialize(@src : Node, @dst : Node, @wt : T) end getter src : Node, dst : Node getter wt : T end def initialize(@size : Node, @inf = 10**9) @g = Array(Array(Edge(T))).new(@size) { [] of Edge(T) } end getter size : Int32 getter inf : T delegate :[], to: @g def add_edge(u : Node, v : Node, wt : T) @g[u] << Edge.new(u, v, wt) end def add_edge_b(u : Node, v : Node, wt : T) @g[u] << Edge.new(u, v, wt) @g[v] << Edge.new(v, u, wt) end end class GraphM(T) alias Node = Int32 def initialize(@size : Int32, @inf = 10**9) @g = Array.new_md(@size, @size, @inf) @size.times do |i| @g[i][i] = T.zero end end getter size : Int32 getter inf : T delegate :[], to: @g def add_edge(u : Node, v : Node, wt : T) @g[u][v] = wt end def add_edge_b(u : Node, v : Node, wt : T) @g[u][v] = @g[v][u] = wt end @g : Array(Array(T)) end class Tree alias Node = Graph::Node def initialize(@g : Graph, @root : Node) size = @g.size @parent = Array.new(size, 0) @children = Array.new(size) { [] of Node } @depth = Array.new(size, -1) @dfs_order = [] of Node s = [{@root, @root}] until s.empty? u, p = s.pop @parent[u] = p @depth[u] = @depth[p] + 1 @dfs_order << u @g[u].each do |v| if v != p @children[u] << v s.push({v, u}) end end end @descendant_size = Array.new(size, 1) @dfs_order.reverse_each do |u| @descendant_size[@parent[u]] += @descendant_size[u] if u != @root end end delegate size, to: @g getter root : Node getter dfs_order : Array(Node) getter parent : Array(Node) getter children : Array(Array(Node)) getter depth : Array(Int32) getter descendant_size : Array(Int32) end class Graph def tree(root) Tree.new(self, root) end end class EulerTour alias Node = Graph::Node def initialize(t : Tree) @path = [] of Node @in_time = Array.new(t.size, 0) @out_time = Array.new(t.size, 0) s = [~t.root, t.root] c = -1 until s.empty? u = s.pop c += 1 if u < 0 @path << ~u @out_time[~u] = c else @path << u @in_time[u] = c children = t.children[u] children.each_with_index do |v, i| s.push(~v) s.push(v) s.push(~u) if i < children.size - 1 end end end end getter path : Array(Node) getter in_time : Array(Int32) getter out_time : Array(Int32) end class Tree def euler_tour EulerTour.new(self) end end solve(ProconIO.new)