import java.math.BigInteger

fun main() {
    readLine()
    val a = readLine()!!.split(" ").map { it.toBigInteger() }

    for (i in 0..60) {
        val x = BigInteger.TWO.pow(i)
        if (a.all { (it + x) == it.xor(x) }) {
            println(x)
            return
        }
    }
}