#include using namespace std; #define int long long #define vvi vector> #define vec vector #define pq priority_queue #define all(v) (v).begin(), (v).end() #define uniqueV(x) sort(x.begin(), x.end()); x.erase(unique(x.begin(), x.end()), x.end()); #define rep(i, n) for (int (i) = (0); (i) < (n); ++(i)) #define repp(i, m, n) for (int (i) = (m); (i) < (n); ++(i)) #define dbg(x) cerr << #x << ": " << x << endl; #define dbg2(x, y) cerr<<"("<<#x<<", "<<#y<<") = "<<"("<(value) << endl; #define line() cerr << "---------------" << endl; const int dx[] = {1, -1, 0, 0}; const int dy[] = {0, 0, -1, 1}; const double PI = 3.14159265358979323846; templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b void printA(vector &printArray, char between = ' ') { int paSize = printArray.size(); for (int i = 0; i < paSize; i++) { cerr << printArray[i] << between;} if (between != '\n') {cerr << endl;} } // ------------------------------------------------------------------------------------------ signed main() { string s; cin >> s; int n = s.size(); if (n % 2) { puts("NO"); return 0; } if (s.substr(0, n/2) == s.substr(n/2, n/2)) { puts("YES"); return 0; } puts("NO"); return 0; }