n,m=gets.split.map(&:to_i)
lc=[]
n.times do
  lc << []
end
n.times do
  b,c=gets.split.map(&:to_i).map{|x|x-1}
  lc[c] << b
end

l=[]
m.times do |i|
  l << i
end
lc.each do |lcc|
  a=0
  lcc.uniq.each.with_index do |ll,i|
    if i==0
      a=ll
      next
    end
    b=ll
    s=[a,b]
    k=a
    while l[k]!=k
      k=l[k]
      s << k
    end
    k=b
    while l[k]!=k
      k=l[k]
      s << k
    end
    min=s.min
    s.uniq do |t|
      l[t]=min if l[t]!=min
    end
  end
end
c=[0]*n
m.times do |i|
  if l[i]!=i&&l[i]!=l[l[i]]
    l[i]=l[l[i]]
  end
  c[l[i]]+=1
end
ans=m
m.times do |i|
  if l[i]==i
    ans-=1
  end
end
puts ans