print((function (f)
	return f(io.stdin:read("*l")) and "YES" or "NO"
end)(function (s)
	if bit.band(#s,1)~=0 then return false end
	local n=bit.rshift(#s,1)
	for i=1,n do if s:sub(i,i)~=s:sub(i+n,i+n) then return false end end
	return true
end))