#include <bits/stdc++.h>
#define rep(i,n) for (int i=0; i<(n); ++i)
using namespace std;
using ll=long long;
int main(){
    string s;
    cin>>s;
    int sl=s.length();
    string s1=s.substr(0,sl/2),s2=s.substr(sl/2,sl);
    cout<<(s1==s2? "YES":"NO")<<endl;
}