import java.util.Scanner

object Main290 {
  def main(args: Array[String]) {
    val sc = new Scanner(System.in)
    val n = sc.nextInt
    val s = sc.next

    val res = s match{
      case ss if ss.length>=4 => "YES"
      case ss if ss.contains("00") ||ss.contains("11") => "YES"
      case _ => "NO"
    }

    println(res)

  }
}