import sys
from itertools import combinations, permutations, product, accumulate, groupby
from collections import defaultdict, deque, Counter
from functools import reduce
import heapq
import bisect
import math
import copy

sys.setrecursionlimit(10 ** 9)
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
INF = float("inf")
MOD = 10 ** 9 + 7
# DFS
# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')


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

    def __str__(self):
        return '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items())
# 0-indexed

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

uf = UnionFind(M)
L = [[] for i in range(N)]
for i in range(N):
    b, c = mi()
    b-=1
    c-=1
    L[c].append(b)

cnt = 0
for l in L:
    for b in l:
        if not uf.same(l[0], b):
            uf.union(l[0], b)
            cnt += 1
print(cnt)