S=input()
n=len(S)
S=list(S)
#print(S)
if(n%2==1):
  print("NO")

else:
    i=0;
    while True:
        if i==int(n/2-1):
           print("YES")
           break
        if S[i]!=S[int(n/2)+i]:
            #  print(S[0])
            #print(S[int(n/2)+i])
           print("NO")
           break
        i=i+1