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