#include <iostream>
#include <iomanip>
#include <vector>
#include <utility>
#include <map>
#include <algorithm>
#include <queue>
#include <cmath>
#include <numeric>
#include <set>

using namespace std;
struct aaa{aaa(){cin.tie(nullptr); ios::sync_with_stdio(false); cout<<fixed<<setprecision(20);};}aaa;
template <class T>ostream &operator<<(ostream &o,const vector<T>&v){o<<"{";for(int i=0;i<(int)v.size();i++)o<<(i>0?", ":"")<<v[i];o<<"}";return o;}
#define debug(v) {cerr<<"\033[1;36m[debug]\033[m "<<#v<<" : "<<v<<endl;}
#define NG {cout<<"NO"<<endl;return 0;}

template<typename T>bool chmax(T a,T& b) {if (b<a) {b=a;return true;} return false;}

using int64 = long long;
using P = pair<int,int>;

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

    if (n%2 != 0) NG;
    
    if (s.substr(0,n/2) == s.substr(n/2, n/2)) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}