#include <iostream>
#include <bitset>
#include <fstream>
#include <string>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <vector>
#include <algorithm>
#include <numeric>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <functional>
#include <cctype>
#include <list>
#include <limits>
//#include <boost/multiprecision/cpp_int.hpp>

const double EPS = (1e-10);


using namespace std;
using Int = long long;
//using namespace boost::multiprecision;

const Int MOD = 1000000007;

Int mod_pow(Int x, Int n) {
    Int res = 1;
    while(n > 0) {
        if(n & 1) res = (res * x) % MOD; //ビット演算(最下位ビットが1のとき)
        x = (x * x) % MOD;
        n >>= 1; //右シフト(n = n >> 1)
    }
    return res;
}


int main(){
    string s; cin >> s;
    string ss;
    if (s.length() % 2 == 0){
        for (int i = s.length()/2; i < s.length(); i++){
            ss.push_back(s[i]);
        }
        for (int i = 0; i < s.length()/2; i++){
            if (s[i] != ss[i]){
                cout << "NO" << endl;
                return 0;
            }
        }
        cout << "YES" << endl;
    }else{
        cout << "NO" << endl;
    }
}