#include "stdio.h"
#include "stdlib.h"

int n, r, t, l;
int* arr1;
int* arr2;

int wait(int time){
    return time%(t*2)<t ? 0 : t*2 - time%(t*2);
}

int min(int a, int b){
    return a<b ? a : b;
}

void swap(){
    int* temp;
    temp = arr1;
    arr1 = arr2;
    arr2 = temp;
}
int main()
{
    scanf("%d%d%d%d", &n, &r, &t, &l);
    int* lamps = (int*)malloc(sizeof(int)*(n+1));
    arr1 = (int*)malloc(sizeof(int)*(n+1));
    arr2 = (int*)malloc(sizeof(int)*(n+1));
    arr1[0] = 0;
    arr2[0] = 0;
    lamps[0] = 0;
    for (int i = 1; i <= n; i++)
    {
        scanf("%d", lamps + i);
        arr1[i] = arr1[i-1] + lamps[i] - lamps[i-1];
        arr1[i] += wait(arr1[i]);
    }
    for (int i = 1; i <= r; i++)
    {
        for (int j = 1; j <= n; j++)
        {
            int distance = lamps[j] - lamps[j-1];
            arr2[j] = min(arr1[j-1] + distance, arr2[j-1] + distance + wait(arr2[j-1] + distance));
        }
        swap();
    }
    printf("%d", arr1[n] + l - lamps[n]);
    free(lamps);
    free(arr1);
    free(arr2);
    return 0;
}