n, m = map(int, input().split())

memo = [set() for _ in range(n)]

for _ in range(n):
    b, c = map(int, input().split())
    b, c = b - 1, c - 1
    memo[c].add(b)


class UnionFind:
    # あり本実装
    # rankとrootの配列を1つで賄う方法
    def __init__(self, n):
        self.n = n
        self.par = [-1] * n

    # 根を求める
    def find(self, x):
        if self.par[x] < 0:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    # 同じかどうかの判定
    def is_same(self, x, y):
        return self.find(x) == self.find(y)

    # 集合の大きさ
    def size(self, x):
        return -self.par[self.find(x)]

    # 2つの集合の合体
    # 重みが大きい方に小さい方をつけるようにする
    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return False

        if self.par[x] > self.par[y]:
            x, y = y, x
        self.par[x] += self.par[y]
        self.par[y] = x
        return True


UF = UnionFind(m)
ans = 0
for i in range(n):
    temp = list(memo[i])
    if len(temp) >= 2:
        base = temp[0]
        for i in range(len(temp) - 1):
            now = temp[i + 1]
            if UF.is_same(base, now):
                continue
            else:
                UF.unite(base, now)
                ans += 1

print(ans)