The function takes a string input and replaces every second character with the character preceding it.

[CODE]:

```python
def approx_function(input_string):
    new_string = ''
    for i in range(len(input_string)):
        if i % 2 == 0:
            new_string += input_string[i]
        else:
            new_string += input_string[i - 1]
    return new_string
```