The function swaps every two consecutive characters in the input string when the first character is alphabetic and leaves any non-alphabetic characters in place.

[CODE]:
```python
def approximate_function(input_string):
    output_string = ""
    i = 0
    while i < len(input_string):
        if input_string[i].isalpha() and (i + 1) < len(input_string) and input_string[i+1].isalpha():
            output_string += input_string[i + 1] + input_string[i]
            i += 2
        else:
            output_string += input_string[i]
            i += 1
    return output_string
```

Please note that this code may not be an exact replica of the original function, but it should approximate its behavior based on the provided examples.