#include <fstream>
#include <iostream>

using namespace std;

#define maxN 500005

int A[maxN], minim[maxN], D;

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

	return sol;
}


int main()
{
	ifstream f("zombie.in");
	ofstream g("zombie.out");
	
	int N, K;
	
	f >> D >> N >> K;
	-- D;
	
	for (int i = 1; i <= N; ++ i)
	{
		f >> A[i];
		
		int j = bin_Search (i);
		
		minim[i] = min (minim[i - 1] + 1, minim[j - 1] + K);
	}
	
	g << minim[N];
	
	return 0;
}