import sys
input = sys.stdin.readline
from collections import *

class Unionfind:
    def __init__(self, n):
        self.par = [-1]*n
        self.rank = [1]*n
    
    def root(self, x):
        r = x
        
        while not self.par[r]<0:
            r = self.par[r]
        
        t = x
        
        while t!=r:
            tmp = t
            t = self.par[t]
            self.par[tmp] = r
        
        return r
    
    def unite(self, x, y):
        rx = self.root(x)
        ry = self.root(y)
        
        if rx==ry:
            return
        
        if self.rank[rx]<=self.rank[ry]:
            self.par[ry] += self.par[rx]
            self.par[rx] = ry
            
            if self.rank[rx]==self.rank[ry]:
                self.rank[ry] += 1
        else:
            self.par[rx] += self.par[ry]
            self.par[ry] = rx
    
    def is_same(self, x, y):
        return self.root(x)==self.root(y)
    
    def count(self, x):
        return -self.par[self.root(x)]

N, M = map(int, input().split())
color = [[] for _ in range(M)]
box = [[] for _ in range(N)]

for _ in range(N):
    b, c = map(int, input().split())
    color[b-1].append(c-1)
    box[c-1].append(b-1)

uf = Unionfind(N)

for i in range(M):
    for j in range(len(color[i])-1):
        uf.unite(color[i][j], color[i][j+1])

s = defaultdict(set)

for i in range(N):
    for b in box[i]:
        s[uf.root(i)].add(b)

ans = 0

for v in s.values():
    ans += len(v)-1

print(ans)