#include<iostream>
#include<string>
#include<stdlib.h>

using namespace std;

void run(){
    string s;
    cin>>s;
    if(s.length()%2==1){
        cout<<"NO"<<endl;
        return;
    }
    else{
        string first = s.substr(0,s.length()/2);
        string latter = s.substr(s.length()/2, s.length());
        if(first==latter){
            cout<<"YES"<<endl;
        }
        else { cout<<"NO"<<endl; }
    }
}

int main()
{
    run();
    return EXIT_SUCCESS;
}