from collections import defaultdict class UnionFind(): def __init__(self, n): self.n = n self.parents = [-1] * n def find(self, x): if self.parents[x] < 0: return x else: self.parents[x] = self.find(self.parents[x]) return self.parents[x] def union(self, x, y): x = self.find(x) y = self.find(y) if x == y: return if self.parents[x] > self.parents[y]: x, y = y, x self.parents[x] += self.parents[y] self.parents[y] = x def size(self, x): return -self.parents[self.find(x)] def same(self, x, y): return self.find(x) == self.find(y) def members(self, x): root = self.find(x) return [i for i in range(self.n) if self.find(i) == root] def roots(self): return [i for i, x in enumerate(self.parents) if x < 0] def group_count(self): return len(self.roots()) def all_group_members(self): group_members = defaultdict(list) for member in range(self.n): group_members[self.find(member)].append(member) return group_members N,M = map(int,input().split()) S = max(N,M) l = [[] for _ in range(N)] uf = UnionFind(S) for i in range(N): b,c = map(int,input().split()) b -= 1 c -= 1 l[c].append(b) for i in range(S): for j in range(len(l[i])-1): uf.union(l[i][j],l[i][j+1]) A = list(uf.all_group_members().values()) group_cnt = len(A) ans = N-group_cnt print(ans)