def main():
    s = input()
    num = [0 for idx in range(26)]

    for i in range(len(s)):
        num[ord(s[i]) - ord('A')] += 1

    for i in range(26):
        if num[i] > 1:
            print("NO")
            return
    print("YES")

if __name__ == '__main__':
    main()