object main{
  object Solver extends InputReader{
    def solve(){
      val sa = getStr()
      val pa = getStr()
      val xa = getStr()

      val sb = getStr()
      val pb = getStr()
      val xb = getStr()

      if(pa == pb){
        println(-1)
      }else if(pa.length < pb.length || (pa.length == pb.length && pa < pb)){
        println(sb)
      }else{
        println(sa)
      }
    }
  }

  // TEMPLATE ------------------------

  def main(args: Array[String]){
    Solver.solve()
  }

  trait InputReader{
    import java.io._
    import java.util._
    protected val stream = System.in
    private val reader = new BufferedReader(new InputStreamReader(stream))
    private var tokenizer = new StringTokenizer(reader.readLine())

    def getStr(): String = {
      while(!tokenizer.hasMoreTokens())
        tokenizer = new StringTokenizer(reader.readLine())
      tokenizer.nextToken()
    }

    def getInt(): Int = getStr().toInt
    def getLong(): Long = getStr().toLong
    def getDouble(): Double = getStr().toDouble
  }
}