val S = readLine()!!

fun judge(S: String): Boolean {
    if (S.length % 2 != 0) return false

    for (i in 0 until S.length / 2) {
        if (S[i] != S[i + S.length / 2]) return false
    }
    return true
}

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