def remove_duplicates(s):
    # Check for invalid characters
    for ch in s:
        if not (ch.isalnum() or ch == " "):
            return "Invalid input"

    seen = set()
    result = []
    for ch in s:
        low = ch.lower()  # case-insensitive comparison
        if low not in seen and ch != " ":
            seen.add(low)
            result.append(ch)
    return "".join(result)


# Driver Code
s = input().strip()
print(remove_duplicates(s))