N,M=map(int,input().split())
par=[i for i in range(N)]
rank=[0]*(N)
friend=[0]*N
block=[0]*N
size=[1]*N
def find(x):
  if par[x]==x:
    return x
  else:
    par[x]=find(par[x])
    return par[x]
 
#同じ集合か判定
def same(x,y):
  return find(x)==find(y)
 
def union(x,y):
  x=find(x)
  y=find(y)
  if x==y:
    return 
  if rank[x]>rank[y]:
    par[y]=x
    size[x]+=size[y]
  else:
    par[x]=y
    size[y]+=size[x]
    if rank[x]==rank[y]:
      rank[y]+=1
 
D={}
for i in range(N):
  a,b=map(int,input().split())
  a-=1
  b-=1
  if b not in D:
    D[b]=[a]
  else:
    D[b].append(a)

for i in D:
  d=D[i]
  for j in range(len(d)-1):
    union(d[j],d[j+1])
E=[0]*N
ans=0
for i in range(N):
  d=find(i)
  if E[d]==0:
    E[d]=1
  else:
    ans+=1
print(ans)