<p>You are given a positive integer <code>num</code> consisting only of digits <code>6</code> and <code>9</code>.</p>

<p>Return <em>the maximum number you can get by changing <strong>at most</strong> one digit (</em><code>6</code><em> becomes </em><code>9</code><em>, and </em><code>9</code><em> becomes </em><code>6</code><em>)</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> num = 9669
<strong>Output:</strong> 9969
<strong>Explanation:</strong> 
Changing the first digit results in 6669.
Changing the second digit results in 9969.
Changing the third digit results in 9699.
Changing the fourth digit results in 9666.
The maximum number is 9969.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> num = 9996
<strong>Output:</strong> 9999
<strong>Explanation:</strong> Changing the last digit 6 to 9 results in the maximum number.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> num = 9999
<strong>Output:</strong> 9999
<strong>Explanation:</strong> It is better not to apply any change.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= num &lt;= 10<sup>4</sup></code></li>
	<li><code>num</code>&nbsp;consists of only <code>6</code> and <code>9</code> digits.</li>
</ul>

class Solution:
    def maximum69Number(self, num: int) -> int:
        # Convert the number to a string
        s = list(str(num))  # Using list so we can mutate individual characters
        
        # Iterate through the digits and change the first '6' to '9'
        for i in range(len(s)):
            if s[i] == '6':
                s[i] = '9'  # Change the first '6' to '9'
                break  # Stop after the first replacement
        
        # Convert the modified list of characters back to an integer
        return int(''.join(s))

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