import java.util.Scanner
object no481{
    def main(args:Array[String]):Unit={
        val scan = new Scanner(System.in)
        var tmp:Int = 1
        for(i <- 1 to 9){
            val get = scan.nextInt
            if( get - tmp == 2 || (i == 1 && get == 2)){
                println(get - 1)
                return
            }
            tmp = get
        }
        println(10)
    }
}