#include <iostream> 
#include<vector>
#include<algorithm>
#include<map>
#include<string>
#include<iomanip>
#include<set>
#include<queue>
#include<deque>
#include<sstream>
#include<cmath>
#include<bitset>
using namespace std;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define req(i,n) for(int i = 1;i <=  n; i++)
#define rrep(i,n) for(int i = n-1;i >= 0;i--)
#define ALL(obj) begin(obj), end(obj)
#define RALL(a) rbegin(a),rend(a)
typedef long long int ll;
typedef long double ld;
template<typename A, size_t N, typename T>
void Fill(A(&array)[N], const T& val) {
    std::fill((T*)array, (T*)(array + N), val);
}
const int inf = 1<<31-1;
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(void) {
    string s; cin >> s;
    if (s.size() % 2) cout << "NO" << endl;
    else {
        if (s.substr(0, s.size() / 2) == s.substr(s.size() / 2, s.size() / 2)) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
}