n = input()
m = len(n)
if m % 2 == 1:
    print("NO")
else:
    l = int(m) / 2
    l = int(l)
    n1 = n[0:l]
    n2 = n[l:]
    for i, value in enumerate(n1):
        if value != n2[i]:
            print("NO")
            break
        else:
            pass
    else:
        print("YES")