fun main() {
    val n = readLine().toInt()
    val array = readLine()
        .split(' ')
        .map { it.toInt() }

    val m = (n / 2) - 1
    var result = 0
    for (i in 0..m) {
        result += kotlin.math.abs(array[i] - array[n - 1 - i])
    }

    println(result)
}