class UnionFind():
    def __init__(self, n):
        self.n = n
        self.par = list(range(self.n))
        self.rank = [1] * n
        self.count = n

    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    def unite(self, x, y):
        p = self.find(x)
        q = self.find(y)
        if p == q:
            return None
        if p > q:
            p, q = q, p
        self.rank[p] += self.rank[q]
        self.par[q] = p
        self.count -= 1

    def same(self, x, y):
        return self.find(x) == self.find(y)

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

    def count(self):
        return self.count
n, m = map(int, input().split())
UF = UnionFind(n)
bc = [list(map(int, input().split())) for i in range(n)]
d = [[] for i in range(n)]
for b, c in bc:
    d[c - 1].append(b - 1)
for i in range(n):
    d[i].sort()
ans = 0
for i in range(n):
    for j in range(len(d[i]) - 1):
        if UF.same(d[i][j], d[i][j + 1]):
            continue
        UF.unite(d[i][j], d[i][j + 1])
        ans += 1
print(ans)