/**
 * @author karayuu
 */
fun main() {
    val list = mutableListOf<Int>()
    for (i in 1..9) {
        readLine()!!.toInt().also { list.add(it) }
    }
    for (i in 1..10) {
        if (list.indexOf(i) == -1) {
            println(i)
            return
        }
    }
}