#include <iostream>
using namespace std;
int main(){
    string s;cin>>s;
    if(s.size()%2==1){
        cout << "NO" << endl;
        return 0;
    }
    for(int i = 0; s.size()/2 > i; i++){
        if(s[i] != s[s.size()/2+i]){
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "YES" << endl;
}