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

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

    size_t size = S.length();
    string S1 = S.substr(0,size/2-1);
    string S2 = S.substr(size/2,size/2-1);
    if(S1.compare(S2) == 0){
        cout << "YES" << endl;
    }else{
        cout << "NO" << endl;
    }
}