#include <iostream>
#include <cstdlib>
#include <vector>
#include <algorithm>
int main()
{
    std::string s;
    std::cin >> s;
    size_t sz = s.size();
    if(sz % 2 != 0){
        std::cout << "NO" << std::endl;
        return 0;
    }
    size_t h = sz / 2;
    for(size_t i = 0; i < h; i++){
        if(s[i] != s[i+h]){
        std::cout << "NO" << std::endl;
        return 0;
        }
    }
    std::cout << "YES" << std::endl;
    return 0;
}