Which is the least amount of time William needs to reach his nest?

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 $X_i$.
 

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
* $1 ≤ R ≤ N ≤ 10000$

* $N < L &le; 10^9$
* $X[i] < L$, for each semaphore
* $X[i] < X[i+1]$ for each $i$ from $0$ to $n-2$

* For tests worth $15$ more points, $R = 0$.
* For tests worth $15$ more points, $N ≤ 20$ and $L ≤ 1000$.
* For tests worth $25$ more points, $N, T ≤ 100$ and $L ≤ 1000$.
* For tests worth $15$ more points, $N ≤ 300$.
 

h2. Exemplu

When William reaches it he finds it red (it just became red), and he will wait since he doesn't have any skip available.

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