#include <bits/stdc++.h>
using namespace std;
 
int main(){
        string S;
        cin >> S;

        bool A = 1;
        if(S.size()%2 == 1){
                A = 0;
        }else{
                for(int i = 0; i < S.size()/2; i++){
                        if(S.at(i)==S.at(S.size()/2 + i)){

                        }else{
                                A = 0;
                                break;
                        }

                }
        }
        if(A == 0){
                cout << "NO" << endl;
        }else{
                cout << "YES" << endl;
        }
}