```python
def long_word(sentence: str) -> str:
    # Split the sentence into words based on spaces
    words = sentence.split()
    # Initialize variables to keep track of the longest word and its length
    longest_word = ""
    longest_length = 0
    
    # Iterate through each word in the list
    for word in words:
        # Update the longest word and its length if the current word is longer
        if len(word) > longest_length:
            longest_word = word
            longest_length = len(word)
    
    # Return the longest word found
    return longest_word
```