#include<iostream>
#include<string>
using namespace std;

int main(){
    string S;
    cin >> S;

    size_t size = S.length();
    string S1 = S.substr(0,size/2);
    string S2 = S.substr(size/2,size/2);
    
    if (size%2 == 0){
        if(S1.compare(S2) == 0){
            cout << "YES" << endl;
        }else{
            cout << "NO" << endl;
        }
    }
    else{
        cout << "NO" << endl;
    }
}