class DSU
  def initialize(n)
    @d = Array(Int32).new(n, -1)
  end

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

  def unite(x, y)
    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 groups
    groups = Hash(Int32, Array(Int32)).new { |h, k| h[k] = [] of Int32 }
    @d.size.times { |i| groups[root(i)] << i }
    groups.values
  end
end

def solve(g, deg, group)
  a = group.select { |i| deg[i] == 0 }
  i = 0
  while i < a.size
    g[a[i]].each { |u| a << u if (deg[u] -= 1) == 0 }
    i += 1
  end
  if group.any? { |i| deg[i] > 0 }
    a = group + [group[0]]
  end
  a.each_cons(2).to_a
end

n, m = read_line.split.map(&.to_i)
g = Array.new(n) { [] of Int32 }
deg = [0] * n
dsu = DSU.new(n)
m.times do
  u, v = read_line.split.map(&.to_i.pred)
  g[u] << v
  deg[v] += 1
  dsu.unite(u, v)
end
ans = dsu.groups.flat_map { |group| solve(g, deg, group) }
puts ans.size, ans.join('\n', &.join ' ', &.succ)