S = input()
kisu = []
gusu = []
if len(S) == 0:
    print("NO")
elif len(S) == 1:
    print("YES")
else:
    for i in range(len(S)):
        if i%2 == 0:
            kisu.append(S[i])
        else:
            gusu.append(S[i])
    moto = int(len(kisu))
    for i in range(len(gusu)):
        if gusu[i] in kisu:
                kisu.remove(gusu[i])
    print(kisu)
    if len(kisu) == moto:
        print("Yes")
    else:
        print("NO")