object Solution {

    def isContains(x: List[Int], y: Map[Int, Int]): Boolean = {
        for (el <- x) {
            if(y.getOrElse(el, 0) <= 1)
                return false
        }
        true
    }

    def main(args: Array[String]) {
        import scala.io.StdIn._
        var n = readInt()
        val buf = Array[(Int, Int)]().toBuffer

        for (_ <- 0 until n) {
            val l = readLine().split(" ").map(_.toInt)
            buf += Tuple2(l(0), l(1))
        }

        val keysX = buf.groupBy(x => x._1).mapValues(_.map(_._2)).toList.filter(x=> x._2.size <= 1).map(_._2).flatten
        

        val keysY = buf.groupBy(x => x._2).mapValues(_.size)
    
        if (isContains(keysX, keysY))
            println("YES")
        else 
            println("NO")
    }
}