N, M = map(int, input().split())
AB = [tuple(map(int,input().split())) for i in range(N)]
graph = [[] for _ in range(N)]
class UnionFind:
    def __init__(self,N):
        self.parent = [i for i in range(N)]
        self._size = [1] * N
        self.count = 0

    def root(self,a):
        if self.parent[a] == a:
            return a
        else:
            self.parent[a] = self.root(self.parent[a])
            return self.parent[a]
    def is_same(self,a,b):
        return self.root(a) == self.root(b)

    def unite(self,a,b):
        ra = self.root(a)
        rb = self.root(b)
        if ra == rb: return
        if self._size[ra] < self._size[rb]: ra,rb = rb,ra
        self._size[ra] += self._size[rb]
        self.parent[rb] = ra
        self.count += 1

    def size(self,a):
        return self._size[self.root(a)]

uf = UnionFind(N)
for a,b in AB:
  a,b = a-1,b-1
  graph[a].append(b)

for g in graph:
  if len(g) >= 2:
    for i in range(len(g)-1):
      uf.unite(g[i], g[i+1])

dp = [-1] * N
for g in graph:
  for gg in g:
    dp[uf.root(gg)] += 1
    break
ans = 0
for e in dp:
  if e >= 1:
    ans += e
  
print(ans)