n,m=map(int,input().split())
g=[[] for i in range(n)]
for i in range(n):
  b,c=map(int,input().split())
  b-=1
  c-=1
  g[c]+=[b]

def root(x):
  p=x
  l=[p]
  while r[p]!=p:
    p=r[p]
    l+=[p]
  for p in l:
    r[p]=l[-1]
  return r[x]

def union(x,y):
  rx=root(x)
  ry=root(y)
  if rx==ry:
    return
  if rx>ry:
    rx,ry=ry,rx
  r[ry]=rx
  return

r=list(range(m))
a=0
for c in range(n):
  for i in range(len(g[c])-1):
    u=g[c][i]
    v=g[c][i+1]
    if root(u)!=root(v):
      union(u,v)
      a+=1

print(a)