#include<iostream>
#include<string>
using namespace std;
int main(){
int a,b=0,c;
string x;
cin>>x;
a=x.size();
if(a%2==1)b=1;
else {
c=a/2;
for(int i=0;i<c;i++){
if(x[i]==x[i+c])b+=0;
else b+=1;
}
}
if(b==0)cout<<"YES"<<endl;
else cout<<"NO"<<endl;
}