lib C
  fun strtoll(s : UInt8*, p : UInt8**, b : Int32) : Int64
end

class String
  def to_i64
    C.strtoll(self, nil, 10)
  end
end

class UnionFind
  @d : Array(Int32)

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

  def root(x : Int32)
    @d[x] < 0 ? x : (@d[x] = root(@d[x]))
  end

  def unite(x : Int32, y : Int32)
    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 : Int32, y : Int32)
    root(x) == root(y)
  end

  def size(x : Int32)
    -@d[root(x)]
  end

  def root?(x : Int32)
    @d[x] < 0
  end
end

n, m = read_line.split.map(&.to_i)
a = (0...n).map { [] of Int32 }
n.times do
  b, c = read_line.split.map(&.to_i.pred)
  a[c] << b
end
uf = UnionFind.new(n)
a.each do |b|
  b.sort.each_cons_pair { |i, j| uf.unite(i, j) }
end
puts (0...n).select { |i| uf.root?(i) }.sum { |i| uf.size(i) - 1 }