class unionfind:
    def __init__(self,n):
      self.n = n
      self.par = [-1]*n
      self.size = [1]*n

    def root(self,x):
         while True:
            if self.par[x] == -1:
                return x
            if self.par[self.par[x]] == -1:
                return self.par[x]
            self.par[x] = self.par[self.par[x]]
            x = self.par[x]

    def unite(self,u,v):
        rootu = self.root(u)
        rootv = self.root(v)
        if rootu != rootv:
            if self.size[rootu] < self.size[rootv]:
                self.par[rootu] = rootv
                self.size[rootv] += self.size[rootu]
            else:
                self.par[rootv] = rootu
                self.size[rootu] += self.size[rootv]

    def same(self,u,v):
        return self.root(u) == self.root(v)

    def siz(self, x):
        return self.size[self.root(x)]

N, M = map(int,input().split())
b = [None]*N 
c = [None]*N
P = [list() for i in range(N)]
for i in range(N):
	b[i], c[i] = map(int,input().split())
	b[i] -= 1 
	c[i] -= 1 
	P[c[i]].append(b[i])

uf = unionfind(M)
ans = 0
for i in range(N):
	if len(P[i]) > 1:
		for x in P[i]:
			if not uf.same(P[i][0],x):
				uf.unite(P[i][0],x)
				ans += 1
print(ans)