object Main {
  import java.io.{BufferedReader, InputStream, InputStreamReader}
  import java.util.StringTokenizer
  import scala.reflect.ClassTag

  def main(args: Array[String]): Unit = {
    val out = new java.io.PrintWriter(System.out)
    new Main(out, new InputReader(System.in)).solve()
    out.flush()
  }

  private[this] val oj = System.getenv("ATCODER_DEBUG") == null
  @inline private final def DEBUG(f: => Unit): Unit = {
    if (!oj){ f }
  }
  @inline private final def debug(as: Array[Boolean]): Unit = if (!oj){ debug(as.map(x => if(x) "1" else "0").mkString) }
  @inline def debug(as: Array[Int]): Unit = if (!oj){ debug(as.mkString(" ")) }
  @inline private final def debug(as: Array[Long]): Unit =if (!oj){ debug(as.mkString(" ")) }
  @inline private final def debugDim(m: Array[Array[Int]]): Unit = if (!oj){
    REP(m.length) { i =>
      debug(m(i))
    }
  }
  @inline private final def debugDimFlip(m: Array[Array[Long]]): Unit = if (!oj){
    REP(m(0).length) { j =>
      REP(m.length) { i =>
        System.err.print(m(i)(j))
        System.err.print(" ")
      }
      System.err.println()
    }
  }
  @inline def debug(s: => String): Unit = DEBUG {
    System.err.println(s)
  }
  @inline private final def debugL(num: => Long): Unit = DEBUG {
    System.err.println(num)
  }
  private def isDebug[A](debug: => A, online: => A): A = {
    if (oj) online else debug
  }

  class InputReader(val stream: InputStream) {
    private[this] val reader = new BufferedReader(new InputStreamReader(stream), 32768)
    private[this] var tokenizer: StringTokenizer = _

    @inline private[this] final def next(): String = {
      while (tokenizer == null || !tokenizer.hasMoreTokens)
        tokenizer = new StringTokenizer(reader.readLine)
      tokenizer.nextToken
    }

    def nextInt(): Int = Integer.parseInt(next())
    def nextLong(): Long = java.lang.Long.parseLong(next())
    def nextChar(): Char = next().charAt(0)

    def ni(): Int = nextInt()
    def nl(): Long = nextLong()
    def nc(): Char = nextChar()
    def ns(): String = next()
    def ns(n: Int): Array[Char] = ns().toCharArray
    def na(n: Int, offset: Int = 0): Array[Int] = map(n)(_ => ni() + offset)
    def na2(n: Int, offset: Int = 0): (Array[Int], Array[Int]) = {
      val A1, A2 = Array.ofDim[Int](n)
      REP(n) { i =>
        A1(i) = ni() + offset
        A2(i) = ni() + offset
      }
      (A1, A2)
    }
    def nm(n: Int, m: Int): Array[Array[Int]] = {
      val A = Array.ofDim[Int](n, m)
      REP(n) { i =>
        REP(m) { j =>
          A(i)(j) = ni()
        }
      }
      A
    }
    def nal(n: Int): Array[Long] = map(n)(_ => nl())
    def nm_c(n: Int, m: Int): Array[Array[Char]] = map(n) (_ => ns(m))
  }

  def REP(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = offset
    val N = n + offset
    while(i < N) { f(i); i += 1 }
  }
  def REP_r(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = n - 1 + offset
    while(i >= offset) { f(i); i -= 1 }
  }
  def TO(from: Int, to: Int)(f: Int => Unit): Unit = {
    REP(to - from + 1, from)(f)
  }
  def map[@specialized A: ClassTag](n: Int, offset: Int = 0)(f: Int => A): Array[A] = {
    val res = Array.ofDim[A](n)
    REP(n)(i => res(i) = f(i + offset))
    res
  }

  def sumL(as: Array[Int]): Long = {
    var s = 0L
    REP(as.length)(i => s += as(i))
    s
  }
  def cumSum(as: Array[Int]): Array[Long] = {
    val cum = Array.ofDim[Long](as.length + 1)
    REP(as.length) { i =>
      cum(i + 1) = cum(i) + as(i)
    }
    cum
  }
}

object Workspace {
  import Main._
  case class Entry(l: Int, r: Int) {
    def segmentLength = Math.max(0, r - l + 1)
  }

  case class L(l: Int, i: Int)
  case class R(r: Int, i: Int)

  class Group(n: Int, E: Array[Entry]) {
    import java.util.Comparator
    private val maxL = new java.util.TreeSet[L](new Comparator[L]{
      override def compare(o1: L, o2: L): Int = {
        if (o1.l == o2.l) Integer.compare(o1.i, o2.i)
        else Integer.compare(o2.l, o1.l)
      }
    })
    private val minR = new java.util.TreeSet[R](new Comparator[R]{
      override def compare(o1: R, o2: R): Int = {
        if (o1.r == o2.r) Integer.compare(o1.i, o2.i)
        else Integer.compare(o1.r, o2.r)
      }
    })

    def add(i: Int): Unit = {
      maxL.add(L(E(i).l, i))
      minR.add(R(E(i).r, i))
    }

    def remove(i: Int): Unit = {
      maxL.remove(L(E(i).l, i))
      minR.remove(R(E(i).r, i))
    }

    def length = maxL.size()

    def segmentLength = {
      val l = maxL.first()
      val r = minR.first()
      debug(s"len l:$l r:$r")
      Math.max(0, r.r - l.l + 1)
    }
  }
}

class Main(out: java.io.PrintWriter, sc: Main.InputReader) {
  import sc._
  import Main._
  import java.util.Arrays.sort

  import scala.collection.mutable
  import math.{abs, max, min}
  import mutable.ArrayBuffer
  import Workspace._

  // toIntとか+7とかするならvalにしろ
  final private[this] val MOD = 1000000007

  def merge(e1: Entry, e2: Entry) = {
    Entry(max(e1.l, e2.l), min(e1.r, e2.r))
  }

  def calcOneG(n: Int, E: Array[Entry]): Int = {
    val LR, RL = Array.ofDim[Entry](n)
    LR(0) = E(0)
    RL(n - 1) = E(n - 1)
    REP(n - 1) { i =>
      LR(i + 1) = Entry(max(LR(i).l, E(i + 1).l), min(LR(i).r, E(i + 1).r))
    }
    REP_r(n - 1) { i =>
      RL(i) = Entry(max(RL(i + 1).l, E(i).l), min(RL(i + 1).r, E(i).r))
    }
    var res = 0
    REP(n) { i =>
      val g2 = if (i == 0) {
        RL(1)
      } else if (i == n - 1) {
        LR(n - 2)
      } else {
        merge(LR(i - 1), RL(i + 1))
      }
      res = max(res, g2.segmentLength + E(i).segmentLength)
    }
    res
  }

  def solve(): Unit = {
    import java.util.Comparator
    val n = ni()
    val E = Array.ofDim[Entry](n)
    REP(n) { i =>
      val l, r = ni()
      E(i) = Entry(l, r)
    }
    sort(E, new Comparator[Entry] {
      override def compare(o1: Entry, o2: Entry): Int = Integer.compare(o2.r, o1.r)
    })
    val maxL = E.map(_.l).max
    val maxLIx = E.zipWithIndex.filter(_._1.l == maxL).maxBy(_._1.r)._2

    debug(s"maxLIx: $maxLIx")
    debug(E.mkString(" "))

    val l = E(maxLIx).l
    var r = E(maxLIx).r

    var ans = calcOneG(n, E)
    val g = new Group(n, E)
    REP(n) { i =>
      if (i != maxLIx) g.add(i)
    }
    REP(n) { i =>
      if (i != maxLIx && g.length > 1) {
        r = min(r, E(i).r)
        g.remove(i)
        debug(s"l:$l r:$r len:${g.segmentLength}")
        val newlen = g.segmentLength + max(0, r - l + 1)
        ans = max(ans, newlen)
      }
    }

    out.println(ans)
  }
}