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