#include <bits/stdc++.h>
using namespace std;
typedef long long  ll;
typedef vector<int> VI;
typedef vector<ll> VLL;
#define rep(i,n) for(int i=0; i<(int)(n); i++)

int main(){
    string s,h;
    cin >> s;
    int size = s.size();

    h = s.substr(0,size/2);
    
    for(int i=size/2; i<size; ++i){
        if(h[i-size/2] != s[i]){
            cout << "NO" << endl;
            return 0;
        }
    }

    cout << "YES" << endl;
    return 0;
}