fun main() {
    val builder = StringBuilder()

    val (n, x) = readInputLine().split(" ").map { it.toLong() }
    val sArr = readInputLine().split(" ").map { it.toLong() }
    val sSum = sArr.sum()

    val wrongA = n * x - sSum

    for (s in sArr) {
        if (s % 2L != 0L) {
            continue
        }
        if (s / 2L + wrongA == x) {
            builder.appendLine(s / 2L)
            break
        }
    }

    print(builder.toString())
}

fun readInputLine(): String {
    return readLine()!!
}