An integer \(N\) (1 ≤ \(N\) ≤ 300000), representing some quantity or size.
An integer \(L\) (1 ≤ \(L\) ≤ 10^9), representing another parameter.
A list of integers \(x\) of size \(N\), where each integer is between 1 and \(L - 1\) and strictly increasing.
A list of integers \(t\) of size \(N\), where each integer is between 1 and 10^9.

### Example Input:
```
2 10
5 8
10 4
```

### Function Signature:
Write a function f(N, L, x, t) that takes in the input.
```python
def f(N: int, L: int, x: List[int], t: List[int]):
    '''
    N: an integer
    L: an integer
    x: a list of integers
    t: a list of integers
    '''
```