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

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

    //cout << s.size() << endl;

    if(s.size() % 2 != 0) {
        cout << "NO" << endl;
        return 0;
    }

    string s1;
    for(int i = 0; i < s.size() / 2; i++){
        s1 += s[i];
    }

    string s2;
    for (int i = s.size() / 2; i < s.size(); i++){
        s2 += s[i];
    }

    //cout << s1 << " " << s2 << endl;

    if(s1 == s2){
        cout << "YES" << endl;
    }else{
        cout << "NO" << endl;
    }
}