object Main{
	def main(args:Array[String]):Unit={
      var input = readLine
      var record:Map[Int,Int] = Map()
      for(i <- input){
        var tmp = i.toString.toInt
        var r = record.getOrElse(tmp,0)
        r+=1
        record+=(tmp -> r)
      }
      var keys = record.keySet.toArray.sorted.reverse
      var flag = true
      var res = ""
      if(keys.length==1){
        for(i <- 0 until 3) res += keys(0).toString
        flag = false
      }
      for(k <- 0 until keys.length if flag){
        if(k==0 && input.charAt(0).toString.toInt==keys(k)){
          for(i <- 0 until 3) res += keys(0).toString
          flag = false
        }
        if(keys(k)==input.charAt(0).toString.toInt){
          for(i <- 0 until 3) res += keys(k-1).toString
          flag = false
        }
      }
      println(res)
      
    }
}