# require "/scanner"
# ### Specifications
#
# ```plain
# Inside input macro                            | Expanded code
# ----------------------------------------------+---------------------------------------
# Uppercase string: Int32, Int64, Float64, etc. | {}.new(Scanner.s)
# s                                             | Scanner.s
# c                                             | Scanner.c
# Other lowercase string: i, i64, f, etc.       | Scanner.s.to_{}
# operator[]: type[size]                        | Array.new(input(size)) { input(type) }
# Tuple literal: {t1, t2, t3}                   | {input(t1), input(t2), input(t3)}
# Array literal: [t1, t2, t3]                   | [input(t1), input(t2), input(t3)]
# Range literal: t1..t2                         | input(t1)..input(t2)
# If: cond ? t1 : t2                            | cond ? input(t1) : input(t2)
# Assign: target = value                        | target = input(value)
# ```
#
# ### Examples
#
# Input:
# ```plain
# 5 3
# foo bar
# 1 2 3 4 5
# ```
# ```
# n, m = input(Int32, Int64) # => {5, 10i64}
# input(String, Char[m])     # => {"foo", ['b', 'a', 'r']}
# input(Int32[n])            # => [1, 2, 3, 4, 5]
# ```
# ```
# n, m = input(i, i64) # => {5, 10i64}
# input(s, c[m])       # => {"foo", ['b', 'a', 'r']}
# input(i[n])          # => [1, 2, 3, 4, 5]
# ```
#
# Input:
# ```plain
# 2 3
# 1 2 3
# 4 5 6
# ```
#
# ```
# h, w = input(i, i) # => {2, 3}
# input(i[h, w])     # => [[1, 2, 3], [4, 5, 6]]
# ```
# ```
# input(i[i][i]) # => [[1, 2, 3], [4, 5, 6]]
# ```
#
# Input:
# ```plain
# 5 3
# 3 1 4 2 5
# 1 2
# 2 3
# 3 1
# ```
# ```
# n, m = input(i, i)       # => {5, 3}
# input(i.pred[n])         # => [2, 0, 3, 1, 4]
# input({i - 1, i - 1}[m]) # => [{0, 1}, {1, 2}, {2, 0}]
# ```
#
# Input:
# ```plain
# 3
# 1 2
# 2 2
# 3 2
# ```
# ```
# input({tmp = i, tmp == 1 ? i : i.pred}[i]) # => [{1, 2}, {2, 1}, {3, 1}]
# ```
class Scanner
  private def self.skip_to_not_space
    peek = STDIN.peek
    not_space = peek.index { |x| x != 32 && x != 10 } || peek.size
    STDIN.skip(not_space)
  end

  def self.c
    skip_to_not_space
    STDIN.read_char.not_nil!
  end

  def self.s
    skip_to_not_space

    peek = STDIN.peek
    if index = peek.index { |x| x == 32 || x == 10 }
      STDIN.skip(index + 1)
      return String.new(peek[0, index])
    end

    String.build do |buffer|
      loop do
        buffer.write peek
        STDIN.skip(peek.size)
        peek = STDIN.peek
        break if peek.empty?
        if index = peek.index { |x| x == 32 || x == 10 }
          buffer.write peek[0, index]
          STDIN.skip(index)
          break
        end
      end
    end
  end
end

macro internal_input(s, else_ast)
  {% if Scanner.class.has_method?(s.id) %}
    Scanner.{{s.id}}
  {% elsif s.stringify == "String" %}
    Scanner.s
  {% elsif s.stringify == "Char" %}
    Scanner.c
  {% elsif s.stringify =~ /[A-Z][a-z0-9_]*/ %}
    {{s.id}}.new(Scanner.s)
  {% elsif String.has_method?("to_#{s}".id) %}
    Scanner.s.to_{{s.id}}
  {% else %}
    {{else_ast}}
  {% end %}
end

macro internal_input_array(s, args)
  {% for i in 0...args.size %}
    %size{i} = input({{args[i]}})
  {% end %}
  {% begin %}
    {% for i in 0...args.size %} Array.new(%size{i}) { {% end %}
      input({{s.id}})
    {% for i in 0...args.size %} } {% end %}
  {% end %}
end

macro input(s)
  {% if s.is_a?(Call) %}
    {% if s.receiver.is_a?(Nop) %}
      internal_input(
        {{s.name}}, {{s.name}}(
          {% for argument in s.args %} input({{argument}}), {% end %}
        )
      )
    {% elsif s.name.stringify == "[]" %}
      internal_input_array({{s.receiver}}, {{s.args}})
    {% else %}
      input({{s.receiver}}).{{s.name.id}}(
        {% for argument in s.args %} input({{argument}}), {% end %}
      ) {{s.block}}
    {% end %}
  {% elsif s.is_a?(TupleLiteral) %}
    { {% for i in 0...s.size %} input({{s[i]}}), {% end %} }
  {% elsif s.is_a?(ArrayLiteral) %}
    [ {% for i in 0...s.size %} input({{s[i]}}), {% end %} ]
  {% elsif s.is_a?(RangeLiteral) %}
    Range.new(input({{s.begin}}), input({{s.end}}), {{s.excludes_end?}})
  {% elsif s.is_a?(If) %}
    {{s.cond}} ? input({{s.then}}) : input({{s.else}})
  {% elsif s.is_a?(Assign) %}
    {{s.target}} = input({{s.value}})
  {% else %}
    internal_input({{s.id}}, {{s.id}})
  {% end %}
end

macro input(*s)
  { {% for s in s %} input({{s}}), {% end %} }
end

# require "atcoder/SCC"
# ac-library.cr by hakatashi https://github.com/google/ac-library.cr
#
# Copyright 2021 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

module AtCoder
  # Implements [atcoder::scc_graph](https://atcoder.github.io/ac-library/master/document_en/scc.html).
  #
  # ```
  # scc = AtCoder::SCC.new(3_i64)
  # scc.add_edge(0, 1)
  # scc.add_edge(1, 0)
  # scc.add_edge(2, 0)
  # scc.scc # => [Set{2}, Set{0, 1}]
  # ```
  class SCC
    alias Adjacency = NamedTuple(in: Array(Int64), out: Array(Int64))

    getter size : Int64
    getter adjacencies : Array(Adjacency)

    def initialize(@size)
      @adjacencies = Array(Adjacency).new(@size) { {in: [] of Int64, out: [] of Int64} }

      @topological_order = Array(Int64).new(@size)
      @visit_counts = Array(Int64).new(@size, 0_i64)
      @visited = Set(Int64).new
      @stack = Deque(Int64).new
      @groups = Array(Set(Int64)).new
    end

    # Implements atcoder::scc_graph.add_edge(from, to).
    def add_edge(from, to)
      @adjacencies[from][:out] << to.to_i64
      @adjacencies[to][:in] << from.to_i64
    end

    private def dfs(start)
      @stack << start
      @visited << start

      until @stack.empty?
        node = @stack.last
        children = @adjacencies[node][:out]

        if @visit_counts[node] < children.size
          child = children[@visit_counts[node]]
          @visit_counts[node] += 1

          unless @visited.includes?(child)
            @visited << child
            @stack << child
          end
        else
          @topological_order << node
          @stack.pop
        end
      end
    end

    private def reverse_dfs(start)
      @stack << start
      @visited << start
      group = Set{start}

      until @stack.empty?
        node = @stack.pop
        children = @adjacencies[node][:in]

        children.each do |child|
          unless @visited.includes?(child)
            @stack << child
            @visited << child
            group << child
          end
        end
      end

      @groups << group
    end

    # Implements atcoder::scc_graph.scc().
    def scc
      @visited = Set(Int64).new
      @stack = Deque(Int64).new
      @visit_counts = Array(Int64).new(@size, 0_i64)
      @topological_order = Array(Int64).new(@size)
      @groups = Array(Set(Int64)).new

      @size.times do |node|
        unless @visited.includes?(node)
          dfs(node)
        end
      end

      @visited = Set(Int64).new

      @topological_order.reverse_each do |node|
        unless @visited.includes?(node)
          reverse_dfs(node)
        end
      end

      @groups
    end
  end
end

# require "/graph/components"
# require "../graph"
# require "./graph/edge"
struct WeightedEdge(T)
  include Comparable(WeightedEdge(T))

  property to : Int32, cost : T

  def initialize(@to, @cost : T)
  end

  def <=>(other : WeightedEdge(T))
    {cost, to} <=> {other.cost, other.to}
  end

  def to_s(io) : Nil
    io << '(' << to << ", " << cost << ')'
  end

  def inspect(io) : Nil
    io << "->#{to}(#{cost})"
  end
end

struct WeightedEdge2(T)
  include Comparable(WeightedEdge2(T))

  property from : Int32, to : Int32, cost : T

  def initialize(@from, @to, @cost : T)
  end

  def initialize(@from, edge : WeightedEdge(T))
    @to, @cost = edge.to, edge.cost
  end

  def <=>(other : WeightedEdge2(T))
    {cost, from, to} <=> {other.cost, other.from, other.to}
  end

  def reverse
    WeightedEdge2(T).new(to, from, cost)
  end

  def sort
    WeightedEdge2(T).new(*{to, from}.minmax, cost)
  end

  def to_s(io) : Nil
    io << '(' << from << ", " << to << ", " << cost << ')'
  end

  def inspect(io) : Nil
    io << from << "->" << to << '(' << cost << ')'
  end
end

struct UnweightedEdge
  property to : Int32

  def initialize(@to)
  end

  def cost
    1
  end

  def to_s(io) : Nil
    io << to
  end

  def inspect(io) : Nil
    io << "->" << to
  end
end

struct UnweightedEdge2
  property from : Int32, to : Int32

  def initialize(@from, @to)
  end

  def initialize(@from, edge : UnweightedEdge)
    @to = edge.to
  end

  def cost
    1
  end

  def reverse
    UnweightedEdge2.new(to, from)
  end

  def sort
    UnweightedEdge2.new(*{to, from}.minmax)
  end

  def to_s(io) : Nil
    io << '(' << from << ", " << to << ')'
  end

  def inspect(io) : Nil
    io << from << "->" << to
  end
end

module Graph(Edge, Edge2)
  include Enumerable(Edge2)

  getter graph : Array(Array(Edge))

  def initialize(size : Int)
    @graph = Array(Array(Edge)).new(size) { [] of Edge }
  end

  def initialize(size : Int, edges : Enumerable)
    initialize(size)
    add_edges(edges)
  end

  # Add *edge*.
  abstract def <<(edge : Edge2)

  # :ditto:
  def <<(edge : Tuple)
    self << Edge2.new(*edge)
  end

  def add_edges(edges : Enumerable)
    edges.each { |edge| self << edge }
  end

  delegate size, to: @graph
  delegate :[], to: @graph

  def each : Nil
    (0...size).each do |v|
      self[v].each do |edge|
        yield Edge2.new(v, edge)
      end
    end
  end

  def reverse
    if self.class.directed?
      each_with_object(self.class.new(size)) do |edge, reversed|
        reversed << edge.reverse
      end
    else
      dup
    end
  end

  def to_undirected
    if self.class.directed?
      each_with_object(self.class.new(size)) do |edge, graph|
        graph << edge
        graph << edge.reverse if self.class.directed?
      end
    else
      dup
    end
  end
end

class DirectedGraph(T)
  include Graph(WeightedEdge(T), WeightedEdge2(T))

  def initialize(size : Int)
    super
  end

  def initialize(size : Int, edges : Enumerable(WeightedEdge2(T)))
    super
  end

  def initialize(size : Int, edges : Enumerable({Int32, Int32, T}))
    super
  end

  def <<(edge : WeightedEdge2(T))
    raise IndexError.new unless 0 <= edge.from < size && 0 <= edge.to < size
    @graph[edge.from] << WeightedEdge.new(edge.to, edge.cost)
    self
  end

  def self.weighted?
    true
  end

  def self.directed?
    true
  end
end

class UndirectedGraph(T)
  include Graph(WeightedEdge(T), WeightedEdge2(T))

  def initialize(size : Int)
    super
  end

  def initialize(size : Int, edges : Enumerable(WeightedEdge2(T)))
    super
  end

  def initialize(size : Int, edges : Enumerable({Int32, Int32, T}))
    super
  end

  def <<(edge : WeightedEdge2(T))
    raise IndexError.new unless 0 <= edge.from < size && 0 <= edge.to < size
    @graph[edge.from] << WeightedEdge.new(edge.to, edge.cost)
    @graph[edge.to] << WeightedEdge.new(edge.from, edge.cost)
    self
  end

  def self.weighted?
    true
  end

  def self.directed?
    false
  end
end

class UnweightedDirectedGraph
  include Graph(UnweightedEdge, UnweightedEdge2)

  def initialize(size : Int)
    super
  end

  def initialize(size : Int, edges : Enumerable)
    super
  end

  def <<(edge : UnweightedEdge2)
    raise IndexError.new unless 0 <= edge.from < size && 0 <= edge.to < size
    @graph[edge.from] << UnweightedEdge.new(edge.to)
    self
  end

  def self.weighted?
    false
  end

  def self.directed?
    true
  end
end

class UnweightedUndirectedGraph
  include Graph(UnweightedEdge, UnweightedEdge2)

  def initialize(size : Int)
    super
  end

  def initialize(size : Int, edges : Enumerable)
    super
  end

  def <<(edge : UnweightedEdge2)
    raise IndexError.new unless 0 <= edge.from < size && 0 <= edge.to < size
    @graph[edge.from] << UnweightedEdge.new(edge.to)
    @graph[edge.to] << UnweightedEdge.new(edge.from)
    self
  end

  def each_child(vertex : Int, parent, &block) : Nil
    graph[vertex].each do |u|
      yield u if u != parent
    end
  end

  def each_child(vertex : Int, parent)
    graph[vertex].each.select { |u| u != parent }
  end

  def self.weighted?
    false
  end

  def self.directed?
    false
  end
end

module Graph(Edge, Edge2)
  # Returns `{components size, index, groups}`.
  def components
    undirected = to_undirected
    index = Array(Int32?).new(size, nil)
    groups = [] of Set(Int32)
    id = 0
    size.times do |v|
      next if index[v]
      que = Deque{v}
      groups << Set(Int32).new
      while u = que.shift?
        next if index[u]
        index[u] = id
        groups[id] << u
        undirected[u].each do |edge|
          que << edge.to if index[edge.to].nil?
        end
      end
      id += 1
    end
    {id, index.map(&.not_nil!), groups}
  end
end

# require "/datastructure/union_find"
class UnionFind
  @d : Array(Int32)

  def initialize(n : Int)
    @d = Array.new(n, -1)
  end

  def initialize(n : Int, edges : Enumerable({Int32, Int32}))
    initialize(n)
    edges.each { |u, v| unite(u, v) }
  end

  def root(x : Int)
    @d[x] < 0 ? x : (@d[x] = root(@d[x]))
  end

  def unite(x : Int, y : Int)
    x = root(x)
    y = root(y)
    return false if x == y
    x, y = y, x if @d[x] > @d[y]
    @d[x] += @d[y]
    @d[y] = x
    true
  end

  def same?(x : Int, y : Int)
    root(x) == root(y)
  end

  def size(x : Int)
    -@d[root(x)]
  end

  def groups
    groups = Hash(Int32, Set(Int32)).new { |h, k| h[k] = Set(Int32).new }
    @d.size.times do |i|
      groups[root(i)] << i
    end
    groups.values.to_set
  end
end

n, m = input(i, i)
edges = input({i - 1, i - 1}[m])
graph = UnweightedDirectedGraph.new n, edges
scc = AtCoder::SCC.new(n.to_i64)
graph.each do |edge|
  scc.add_edge edge.from, edge.to
end

scc_groups = scc.scc.map &.map(&.to_i)
scc_id = [-1] * n
scc_groups.each_with_index do |group, id|
  group.each { |i| scc_id[i] = id }
end
k, id, groups = graph.components

ans = [] of {Int32, Int32}

has_cycle = [false] * k
scc_groups.each do |group|
  v = group.first
  has_cycle[id[v]] = true if group.size > 1
end

topo = Array.new(k) { [] of Int32 }
scc_groups.each do |group|
  group.each do |v|
    topo[id[v]] << v
  end
end

(0...k).each do |i|
  group = groups[i].to_a
  if has_cycle[i]
    (0...group.size).each do |i|
      ans << {group[i], group[i.succ % group.size]}
    end
  else
    topo[i].each_cons_pair do |u, v|
      ans << {u, v}
    end
  end
end

puts ans.size, ans.join('\n', &.join(' ', &.succ))