h2. Date de intrare

The first line of the input file $police.in$ contains 4 integers: $N$ (the number of semaphores), $R$ (the number of semaphores William can skip), $T$ (the half-period of the semaphores), and $L$ (the length of the street).
The second line contains $N$ integers: the coordinates X[i].

h2. Date de ieşire
The output file $police.out$ contains a single line with an integer: the minimum time in seconds that will be needed to reach the nest.

h2. Restricţii
* $1 ≤ R ≤ N ≤ 10000$