val S = readLine()!!

fun judge(S: String): Boolean {
    val n = S.length
    val m = n / 2

    if (n % 2 != 0 || S.slice(0 until m) != S.slice(m until n)) {
        return false
    }
    return true
}

fun main(args: Array<String>) {
    println(if (judge(S)) "YES" else "NO")
}