//include //------------------------------------------ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; //conversion //------------------------------------------ inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; } template inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); } //math //------------------------------------------- template inline T sqr(T x) { return x*x; } //typedef //------------------------------------------ typedef vector VI; typedef vector VVI; typedef vector VS; typedef pair PII; typedef long long LL; //container util //------------------------------------------ #define ALL(a) (a).begin(),(a).end() #define RALL(a) (a).rbegin(), (a).rend() #define PB push_back #define MP make_pair #define SZ(a) int((a).size()) #define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i) #define EXIST(s,e) ((s).find(e)!=(s).end()) #define EXISTch(s,c) ((((s).find_first_of(c)) != std::string::npos)? 1 : 0)//cがあれば1 if(1) #define SORT(c) sort((c).begin(),(c).end()) //repetition //------------------------------------------ #define FOR(i,a,b) for(int i=(a);i<(b);++i) #define rep(i,n) FOR(i,0,n) #define loop(n) FOR(i,0,n) #define rrep(i,a,b) for(int i=(a);i>=(b);--i) //constant //-------------------------------------------- const double EPS = 1e-10; const double PI = acos(-1.0); const int INF = (int)1000000007; const LL MOD = (LL)1000000007;//10^9+7 const LL INF2 = (LL)100000000000000000;//10^18 int main() { string s; cin >> s; if (s.length() % 2 == 1) { cout << "NO" << endl; return 0; } for (int i = 0; i < s.length() / 2; i++) { if (s[i] != s[s.length() / 2 + i]) { cout << "NO" << endl; return 0; } } cout << "YES" << endl; return 0; }