import java.io.PrintWriter
import java.util.*

fun PrintWriter.solve() {
    val n = nextInt()
    val x = nextLong()
    val s = Array(n) { nextLong() }
    val sum = s.sum()
    for (i in 0 until n) {
        if (s[i] % 2 != 0L) continue
        val v = sum - s[i] / 2
        if ((n - 1) * x == v) {
            println(s[i] / 2)
            return
        }
    }
}

fun main() {
    val writer = PrintWriter(System.out, false)
    writer.solve()
    writer.flush()
}

// region Scanner
private var st = StringTokenizer("")
private val br = System.`in`.bufferedReader()

fun next(): String {
    while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine())
    return st.nextToken()
}

fun nextInt() = next().toInt()
fun nextLong() = next().toLong()
fun nextLine() = br.readLine()!!
fun nextDouble() = next().toDouble()
// endregion