using namespace std;
#include <fstream>
ifstream fin("zombie.in");
ofstream fout("zombie.out");
int n,d,k,x[1000005],c[1000005],start;
int main()
{
	int i,sk;
	fin>>d>>n>>k;
	for(i=1;i<=n;i++)
		fin>>x[i];	
	
	for(i=1;i<=k;i++)
		c[i]=i;	
	sk=x[k]-x[1]+1;start=1;
	for(i=k+1;i<=n;i++)
		if(sk+x[i]-x[i-1]>=d)
			{
			sk=x[i]-x[i-k+1]+1;
			c[i]=c[i-1]+1;
			start=i;	
		}
		else
			{
			sk=sk+x[i]-x[i-1];
			c[i]=c[start];
			}
		
	fout<<c[n]<<"\n";
	return 0;
}