#include <bits/stdc++.h>
using namespace std;
 
int main() {
    string S;
    cin >> S;
    int s=S.size();
    if(s%2==1){cout << "NO" << endl;}
    else{
        if(S.substr(0,s/2)==S.substr(s/2,s/2)){cout << "YES" << endl;}
        else{cout << "NO" << endl;}
    }
}