class UnionFind:
    def __init__(self, size):
        self.data = [-1] * size
    def root(self, x):
        if self.data[x] < 0:
            return x
        ans = self.root(self.data[x])
        self.data[x] = ans
        return ans
    def unite(self, x, y):
        x = self.root(x)
        y = self.root(y)
        if x == y:
            return False
        if self.data[x] > self.data[y]:
            x, y = y, x
        self.data[x] += self.data[y]
        self.data[y] = x
        return True
    def is_root(self, x):
        return self.data[x] < 0
    def size(self, x):
        return -self.data[self.root(x)]

n, m = map(int, input().split(' '))
assert 1 <= n <= 200000
assert 1 <= m <= 200000

uf = UnionFind(n + m) # n + i に色 i の超頂点をおく
for i in range(n):
    b, c = map(int, input().split(' '))
    assert 1 <= b <= m
    assert 1 <= c <= n
    b -= 1
    c -= 1
    uf.unite(b, m + c)

ans = 0
for i in range(n + m):
    if uf.is_root(i):
        ans += uf.size(i) - 1
for i in range(m, m + n): # 超頂点の分足しすぎるので、引く
    if uf.size(i) > 1:
        ans -= 1

print(ans)