#include <iostream>
#include <cstdio>

using namespace std;

#define maxN 1000005

int A[maxN], minim[maxN];

int bin_Search (int x, int dist)
{
	int st = 1, dr = x, mid;
	if (x - dist - 1 >= 1) st = x - dist - 1;
	int sol = maxN;
	
	while (st <= dr)
	{
		mid = (st + dr) / 2;
		
		if (A[x] - A[mid] > dist) st = mid + 1;
		else
		{
			sol = min (sol, mid);
			dr = mid - 1;
		}
	}

	return sol;
}


int main()
{
	freopen ("zombie.in", "r", stdin);
	freopen ("zombie.out", "w", stdout);
	
	int D, N, K;
	
	scanf ("%d %d %d", &D, &N, &K);
	
	for (int i = 1; i <= N; ++ i)
	{
		scanf ("%d", &A[i]);
		
		int j = bin_Search (i, D - 1);
		
		minim[i] = min (minim[i - 1] + 1, minim[j - 1] + K);
	}
	
	printf ("%d", minim[N]);
	
	return 0;
}