#include <fstream>
#include <queue>

const int NMAX = 1000005;

using namespace std;
ifstream f("zombie.in");
ofstream g("zombie.out");

int N,D,K,cost_min,it;
long long sol[NMAX],v[NMAX];
queue <int> Q;

long long minim(long long a, long long b)
{
	if (a < b)
		return a;
	return b;
}

int main()
{
	f >> D >> N >> K;
	
	//it = 1;
	
	for (int i = 1; i <= N; ++i)
	{
		f >> v[i];
		Q.push(v[i]);
		while (v[i] - Q.front() >= D)
		{
			Q.pop();
			it++;
		}
		sol[i] = minim(sol[i-1]+1, sol[it] + K);
	}
	
	g << sol[N];
	
	f.close();
	g.close();
	return 0;
}