import java.io.BufferedReader
import java.io.InputStream
import java.io.InputStreamReader
import java.lang.AssertionError
import java.util.*
import kotlin.math.abs
import kotlin.math.max
import kotlin.math.min

val MOD = 1_000_000_007

class UnionFind(n: Int) {
  private val par = IntArray(n){it}
  private val rank = IntArray(n){1} // 集合の要素数
  private val visits = IntArray(n) // 訪れた場所をfind毎に用意するのがもったいないのでつかいまわす

  fun find(x: Int): Int {
    var ptr = 0
    var i = x
    while(par[i] != i) {
      visits[ptr++] = i
      i = par[i]
    }

    for (j in 0 until ptr) {
      par[visits[j]] = i
    }
    return i
  }

  private fun merge(node: Int, rt: Int): Int {
    par[node] = rt
    rank[rt] += rank[node]
    return rt
  }

  fun unite(x: Int, y: Int): Boolean {
    val x1 = find(x)
    val y1 = find(y)
    return if (x1 == y1) false
    else {
      if (rank[x1] < rank[y1])
        merge(x1, y1)
      else
        merge(y1, x1)

      true
    }
  }

  fun isSame(x: Int, y: Int) = find(x) == find(y)

  fun isRoot(x: Int) = par[x] == x

  /**
   * xを解決する必要がないときは直にrankをみる
   */
  fun cntNodes(x: Int): Int = rank[find(x)]

  fun inspect() = run{par}
}
class Solver(stream: InputStream, private val out: java.io.PrintWriter) {
  private val reader = BufferedReader(InputStreamReader(stream), 32768)

  fun solve() {
    val N = ni()
    val MAX = 2e5.toInt()
    val degreeIn = IntArray(MAX)
    val degreeOut = IntArray(MAX)
    val uf = UnionFind(MAX)
    val (from, to) = na2(N, -1)
    val unq = mutableSetOf<Int>()
    for (i in 0 until N) {
      val v = from[i]
      val u = to[i]
      degreeIn[v]++
      degreeOut[u]++
      unq += v
      unq += u
      uf.unite(v, u)
    }

    val diff = (0 until MAX).map{ degreeIn[it] - degreeOut[it] }

    debug{"unq:${unq}"}

    fun isSemi() = run {
      diff.count { it == 1 } == 1 &&
          diff.count { it == -1 } == 1 &&
          diff.count { it == 0 } == MAX - 2
    }

    val ans = if (uf.cntNodes(from[0]) < unq.size) 0
    else if (diff.count { it == 0 } == MAX) {
      degreeIn.count { it > 0 }
    }
    else if (isSemi()) 1
    else 0

    out.println(ans)
  }













































  private val isDebug = try {
    // なんか本番でエラーでる
    System.getenv("MY_DEBUG") != null
  } catch (t: Throwable) {
    false
  }

  private var tokenizer: StringTokenizer? = null
  private fun next(): String {
    while (tokenizer == null || !tokenizer!!.hasMoreTokens()) {
      tokenizer = StringTokenizer(reader.readLine())
    }
    return tokenizer!!.nextToken()
  }

  private fun ni() = next().toInt()
  private fun nl() = next().toLong()
  private fun ns() = next()
  private fun na(n: Int, offset: Int = 0): IntArray {
    return IntArray(n) { ni() + offset }
  }
  private fun nal(n: Int, offset: Int = 0): LongArray {
    val res = LongArray(n)
    for (i in 0 until n) {
      res[i] = nl() + offset
    }
    return res
  }

  private fun na2(n: Int, offset: Int = 0): Array<IntArray> {
    val a  = Array(2){IntArray(n)}
    for (i in 0 until n) {
      for (e in a) {
        e[i] = ni() + offset
      }
    }
    return a
  }

  private inline fun debug(msg: () -> String) {
    if (isDebug) System.err.println(msg())
  }

  /**
   * コーナーケースでエラー出たりするので、debug(dp[1])のように添え字付きの場合はdebug{}をつかうこと
   */
  private inline fun debug(a: LongArray) {
    debug { a.joinToString(" ") }
  }

  private inline fun debug(a: IntArray) {
    debug { a.joinToString(" ") }
  }

  private inline fun debug(a: BooleanArray) {
    debug { toString(a) }
  }

  private inline fun toString(a: BooleanArray) = run{a.map { if (it) 1 else 0 }.joinToString("")}

  private inline fun debugDim(A: Array<LongArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }
  private inline fun debugDim(A: Array<IntArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }
  private inline fun debugDim(A: Array<BooleanArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }

  /**
   * 勝手にimport消されるのを防ぎたい
   */
  private fun hoge() {
    min(1, 2)
    max(1, 2)
    abs(-10)
  }

  private inline fun assert(b: Boolean) = run{if (!b) throw AssertionError()}
  private inline fun assert(b: Boolean, f: () -> String) = run{if (!b) throw AssertionError(f())}
}

fun main() {
  val out = java.io.PrintWriter(System.out)
  Solver(System.`in`, out).solve()
  out.flush()
}