#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    string S;
    cin >> S;
    int l = S.length();
    if(l % 2 == 0 && S.substr(l/2) == S.substr(0,l/2)){
        cout << "YES" << endl;
    }else{
        cout << "NO" << endl;
    }
}