class UnionFindVerSize():
    def __init__(self, N):
        self._parent = [n for n in range(0, N)]
        self._size = [1] * N

    def find_root(self, x):
        if self._parent[x] == x: return x
        self._parent[x] = self.find_root(self._parent[x])
        return self._parent[x]

    def unite(self, x, y):
        gx = self.find_root(x)
        gy = self.find_root(y)
        if gx == gy: return

        if self._size[gx] < self._size[gy]:
            self._parent[gx] = gy
            self._size[gy] += self._size[gx]
        else:
            self._parent[gy] = gx
            self._size[gx] += self._size[gy]

    def get_size(self, x):
        return self._size[self.find_root(x)]

    def is_same_group(self, x, y):
        return self.find_root(x) == self.find_root(y)

    def calc_group_num(self):
        N = len(self._parent)
        ans = 0
        for i in range(N):
            if self.find_root(i) == i:
                ans += 1
        return ans

import sys

N,M = map(int,input().split())

assert(1<=N<=2*10**5)
assert(1<=M<=2*10**5)

b = [-1]*N
c = [-1]*N

for i in range(N):
    b[i],c[i] = map(int,input().split())

assert(all(1<=b[i]<=M for i in range(N)))
assert(all(1<=c[i]<=N for i in range(N)))

box = [[] for i in range(M+1)]
color = [0 for i in range(N)]

for i in range(N):
    box[b[i]].append(c[i]-1)
    color[c[i]-1] += 1

uf = UnionFindVerSize(N)
for i in range(M+1):
    for v in box[i]:
        uf.unite(v,box[i][0])

none_color = sum(int(color[i]==0) for i in range(N))

connected = uf.calc_group_num() - none_color

B = sum(int(box[i]!=[]) for i in range(M+1))

print(B-connected)