#include <algorithm>
#include <stdio.h>

#define MAX 20

using namespace std;

int n, d, k;
int sol[MAX], a[MAX];

int main()
{
	freopen("zombie.in", "r", stdin);
	freopen("zombie.out", "w", stdout);

	scanf("%d %d %d", &d, &n, &k);

	for (int i = 1; i <= n; i++)
		scanf("%d\n", &a[i]);

	int pr = 0;
	for (int i = 1; i <= n; i++)
	{
		for (; a[pr + 1] <= a[i] - d; pr++);

		sol[i] = min(sol[pr] + k, sol[i - 1] + 1);
	}

	printf("%d\n", sol[n]);

	return 0;
}