# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')
import sys
from itertools import combinations, permutations, product, accumulate, groupby
from collections import defaultdict, deque, Counter
from functools import reduce
from operator import add, mul
import heapq
import bisect
import math
import copy

# sys.setrecursionlimit(10 ** 7)
input = lambda: sys.stdin.readline().rstrip()
INF = float("inf")
MOD = 10 ** 9 + 7

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

    def __str__(self):
        return '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items())
N, M = map(int, input().split())
L = [[] for i in range(N+1)]

for i in range(N):
    b, c = map(int, input().split())
    L[c].append(b)

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