#include <bits/stdc++.h>
using namespace std;

int main()
{
    int flag = 0;
    string s;
    cin >> s;

    if(s.length() % 2 != 0) flag = 1;
    for(int i = 0; i < s.length() / 2; i++){
        if(s[i] != s[s.length() / 2 + i]) flag = 1;
    }

    cout << (flag == 0 ? "YES" : "NO") << endl;

    return 0;
}