function Main(input){
	input = input.split("\n")[0];
	var len = input.length;
  if(len % 2 == 1)return "NO\n";
  var a = len / 2;
  for(var i = 0; i < a; i++){
  	if(input[i] !== input[i+a]){
    	return "NO\n";
    }
  }
  return "YES\n";
}

console.log(Main(require("fs").readFileSync("/dev/stdin", "utf8")));