#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep3(i, l, n) for (int i = l; i < n; ++i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define out(a) cout << a << endl
#define SZ(v) (int)v.size()
#define inf (int)(1e9+7)

int main() {
    string s; cin >> s;
    if (SZ(s) % 2 == 1) { out("NO"); return 0; }
    string t = s.substr(SZ(s) / 2, SZ(s) / 2);
    s = s.substr(0, SZ(s) / 2);
    if (s == t) out("YES");
    else out("NO");
}