import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}

void main()
{
  string s; readV(s);
  auto n = s.length;
  writeln(n%2 == 1 || s[0..n/2] != s[n/2..$] ? "NO" : "YES");
}