#include <bits/stdc++.h>
#define show(x) std::cerr << #x << " = " << x << std::endl
using ll = long long;
using ull = unsigned long long;
using ld = long double;
constexpr ll MOD = 1000000007LL;
template <typename T>
constexpr T INF = std::numeric_limits<T>::max() / 10;
std::mt19937 mt{std::random_device{}()};
int main()
{
    std::string s;
    std::cin >> s;
    std::cout << (s.substr(0, s.size() / 2) == s.substr(s.size() / 2, s.size() - s.size() / 2) ? "YES" : "NO") << std::endl;
    return 0;
}