#include<bits/stdc++.h>
using namespace std;
#define ALL(obj) (obj).begin(), (obj).end()
#define FOR(i, a, b) for(int i = (a); i < (b); ++i)
#define REP(i, n) for(int i = 0; i < (n); ++i)

#define endl "\n"
#define pb push_back
#define elif else if
#define cout_db cout << fixed

#define MOD 1000000007
 
const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1};
const int dx_8[]={1,1,0,-1,-1,-1,0,1}, dy_8[]={0,-1,-1,-1,0,1,1,1};

typedef long long ll;

template <typename T>
inline T GCD(T a,T b){T c;while(b!=0){c=a%b;a=b;b=c;}return a;}
template <typename T>
inline T LCM(T a,T b){T c=GCD(a,b);a/=c;return a*b;}
template <typename T>
inline T nCr(T a,T b){T i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
template <typename T>
inline T nHr(T a,T b){return nCr(a+b-1,b);}
template <typename T>
inline T POW(T a,T b){int i,r=1;for(i=1;i<=b;i++){r*=a;}return r;}

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

	string s, ans;
	cin >> s;

	if(s.size() % 2 != 0) ans = "NO";
	else{
		string t = s.substr(0, s.size()/2);
		string u = s.substr(s.size()/2, s.size()/2);
		if(t != u) ans = "NO";
		else ans = "YES";
	}
	cout << ans << endl;

	return 0;
}