import kotlin.collections.*
import kotlin.math.*

@kotlin.ExperimentalStdlibApi
fun main() {
    val (n, m) = readLine()!!.split(" ").map { it.toInt() }
    val uni = UnionFind(m)

    val c2b = mutableMapOf<Int, Int>()
    var ans = 0
    for (i in 0 until n) {
        val (b, c) = readLine()!!.split(" ").map { it.toInt() }
        val box = c2b.get(c)

        when (box) {
            null -> c2b[c] = b
            else -> {
                if (uni.isSame(box, b)) continue
                ans++
                c2b[c] = uni.root(b)
            }
        }
    }

    println(ans)
}

data class UnionFind(private val n : Int) {
    private data class node(var parent : Int? = null, var size : Int = 1)
    private val nodes = Array(n+1) { node() }

    fun root(x : Int): Int {
        return when(nodes[x].parent) {
            null -> x
            else -> { nodes[x].parent = root(nodes[x].parent!!); nodes[x].parent!! }
        }
    }

    fun merge(x : Int, y : Int) : Boolean{
        var rx = root(x); var ry = root(y)
        if (rx == ry) return false
        if (nodes[rx].size < nodes[ry].size) rx = ry.also { ry = rx }
        nodes[ry].parent = rx; nodes[rx].size += nodes[ry].size
        return true
    }
    fun isSame(x : Int, y : Int) : Boolean { return root(x) == root(y) }
    fun size(x : Int) : Int { return nodes[root(x)].size }
}