#include <fstream>
#define NMAX 1000005
using namespace std;
int d,n,k,A[NMAX],D[NMAX];
inline int min(int x,int y)
{
	return x<y ? x : y;
}
ifstream in("zombie.in");
ofstream out("zombie.out");
int main()
{
	in>>d>>n>>k;
	int i,poz;
	for (i=1; i<=n; i++)
		in>>A[i];
	poz=1;
	for (i=1; i<=n; i++)
	{
		while (A[i]-(d-1)>A[poz])
			poz++;
		D[i]=min(D[i-1]+1,D[poz-1]+k);
	}
	out<<D[n]<<'\n';
	return 0;
}