package main

import . "fmt"
import . "os"
import bf "bufio"
import . "sort"

func main() {
	rd:=bf.NewReader(Stdin)
	var n,m int
	Fscan(rd,&n,&m)
	table := make([][]int, n+1)
	for i := 0; i < n; i++ {
		var b, c int
		Fscan(rd,&b,&c)
		table[c] = append(table[c], b)
	}
	Slice(table, func(i, j int) bool {
		return len(table[j])<len(table[i])
	})
	ans := 0
	for _, bs := range table {
		for i := 0; i < len(bs)-1; i++ {
			if isSame(bs[i],bs[i+1]) {
				continue
			}
			union(bs[i],bs[i+1])
			ans++
		}
	}
	Println(ans)
}

var group [2e5+10]int
var place [2e5+10]int
var groupId int = 0

func getGroup(a int) int {
	g := place[a]
	for g != group[g] {
		g = group[g]
	}
	place[a] = g
	return g
}

func isSame(a, b int) bool {
	ga := getGroup(a)
	gb := getGroup(b)
	return ga != 0 && ga == gb
}

func union(a, b int) {
	ga := getGroup(a)
	gb := getGroup(b)
	switch {
		case ga == 0 && gb == 0:
			groupId++
			place[a] = groupId
			place[b] = groupId
			group[groupId] = groupId
		case ga == 0:
			place[a] = gb
		case gb == 0:
			place[b] = ga
		default:
			ga,gb = min(ga,gb),max(ga,gb)
			group[gb] = ga
	}
}


/*
考察

UnionFind使う問題ぽく感じる
実装うろ覚えなのでうまくいくか・・・？

WAした理由が予想つかない
難問だ

*/