import java.util.Scanner

object Problem290 {

  def proc(N: Int, S: String): String = {

    val result = N match {
      case 1 => false
      case 2 => S(0) == S(1)
      case 3 => S(0) == S(1) || S(1) == S(2)
      case _ => true
    }

    result match {
      case true => "YES"
      case false => "NO"
    }
  }

  def main(args: Array[String]) {
    val sc = new Scanner(System.in)
    val N = sc.nextInt()
    val S = sc.next()

    val result = proc(N, S)
    println(result)
  }
}