The function takes a string input and increments the ASCII value of each character by the same fixed value, skipping each second character in the input string. For example, when input is "apple", the function outputs "axxnl".

[CODE]:

```python
def f(x):
    result = ""
    for idx, char in enumerate(x):
        if idx % 2 == 0:
            result += chr(ord(char)+1)
        else:
            result += char
    return result
```
