S=input()
if len(S)%2!=0:
    print("NO")
elif len(S)!=2 and S[0:int((len(S)/2)-1)]==S[int((len(S)/2)):len(S)-1]:
    print("YES")
elif len(S)==2:
    if S[0]==S[1]:
        print("YES")
    else:
        print("NO")
    
else:
    print("NO")