let S = readLine()!
var c = S.count
let s0 = S[S.index(S.startIndex, offsetBy: 0)...S.index(S.startIndex, offsetBy: c / 2 - 1)]
let s1 = S[S.index(S.startIndex, offsetBy: c / 2)...S.index(S.startIndex, offsetBy: c-1)]
print(s0 == s1 ? "YES" : "NO")