#include <iostream>
#include <string>
#include <vector>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <stack>
#include <istream>
#include <map>
#include <set>
#include <queue>
#define rep0(i,n) for (int i = 0; i < (n); ++i)
#define rep1(i,n) for (int i = 1; i < (n); ++i)
#define REP(i,a,b) for (int i = a; i < (b); ++i) 
const long long INF = 1000000007;
typedef long long ll;
using namespace std;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
int main() {
cin.tie(0);
ios::sync_with_stdio(false);
/*
/
/
/
*/
	string s;cin>>s;
	int ssize = s.length();
	string tempa,tempb;
	if(ssize % 2 != 0){puts("NO");return 0;}
	else{
	    rep0(i,ssize){
	        if(i <ssize / 2){
	            tempa += s[i];
	        }
	        else{
	            tempb += s[i];
	        }
	    }
	}
	if(tempb == tempa)puts("YES");
	else puts("NO");
    return 0;
}