import java.io.PrintWriter
import java.util.*

class UnionFind(n: Int) {
    private val rank = IntArray(n) { 0 }
    private val parent = IntArray(n) { -1 }

    fun find(x: Int): Int {
        if (parent[x] < 0) {
            return x
        }
        parent[x] = find(parent[x])
        return parent[x]
    }

    fun unite(x: Int, y: Int) {
        val x1 = find(x)
        val y1 = find(y)
        if (x1 == y1) {
            return
        }
        if (rank[x1] < rank[y1]) {
            parent[y1] += parent[x1]
            parent[x1] = y1
        } else {
            parent[x1] += parent[y1]
            parent[y1] = x1
            if (rank[x1] == rank[y1]) {
                rank[x1]++
            }
        }
    }

    fun same(x: Int, y: Int): Boolean {
        return find(x) == find(y)
    }

    fun size(x: Int): Int {
        return -parent[find(x)]
    }
}

fun PrintWriter.solve() {
    val n = nextInt()
    val m = nextInt()
    val (b, c) = Array(n) { nextInt() - 1 to nextInt() - 1 }.unzip().toList().map { it.toTypedArray() }
    val boxes = Array(n) { mutableSetOf<Int>() }
    for (i in 0 until n) {
        boxes[c[i]].add(b[i])
    }
    val uf = UnionFind(m)
    for (set in boxes) {
        if (set.size <= 1) continue
        val u = set.first()
        for (v in set) {
            uf.unite(u, v)
        }
    }
    val par = (0 until m).map { uf.find(it) }.distinct()
    val size = par.map { uf.size(it) }
    println(size.map { it - 1 }.sum())
}

fun main() {
    val writer = PrintWriter(System.out, false)
    writer.solve()
    writer.flush()
}

// region Scanner
private var st = StringTokenizer("")
private val br = System.`in`.bufferedReader()

fun next(): String {
    while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine())
    return st.nextToken()
}

fun nextInt() = next().toInt()
fun nextLong() = next().toLong()
fun nextLine() = br.readLine()!!
fun nextDouble() = next().toDouble()
// endregion