let input:String = readLine()!
if input.count % 2 != 0 {
    print("NO")
}
else {
    let prefix:String = String(input.prefix(input.count / 2))
    let suffix:String = String(input.suffix(input.count / 2))
    if prefix == suffix {
        print("YES")
    }
    else {
        print("NO")
    }
}