#include <bits/stdc++.h>
#define rep(i, n) for (ll i = 0; i < n; ++i)
typedef long long ll;
using namespace std;
const int INF = 1e9;

int main() {
    string s;
    cin >> s;

    bool flag = true;
    if (s.size() % 2 == 1)
        flag = false;
    else {
        rep(i, s.size() / 2) {
            if (s[i] != s[s.size() / 2 + i])
                flag = false;
        }
    }

    flag ? cout << "YES" : cout << "NO";
    cout << endl;

    return 0;
}