#import sys

#print(sys.argv[1])
#text=sys.argv[1]
#leng= (len(sys.argv[1]))
#print(leng)

first = input()
print(first)
leng= (len(first))
lengheaf= (len(first)//2)
#lengheaf= (leng//2)
#print(lengheaf)

#print("比較開始")
#print(text[0: lengheaf])
#print(text[lengheaf:leng])

#if text[0: lengheaf] == text[lengheaf:leng]:
if first[0: lengheaf] == first[lengheaf:leng]:
    print("yes")
else:
    print("no")