#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<unordered_map>
#include<climits>
#include<cstdlib>
#include<cmath>
#include<string>
#include<iomanip>

using namespace std;

#define INF 1 << 29
#define LL long long int

LL const MOD = 1000000007;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    string str;
    cin >> str;
    if(str.size()%2 == 0){
        if(str.substr(0,str.size()/2) == str.substr(str.size()/2,str.size()/2)){
            cout << "YES" << endl;
        }else{
            cout << "NO" << endl;
        }
    }else{
        cout << "NO" << endl;
    }
    
    return 0;
}