import java.util.*;
class jobschedule {
static int n, d, m;
static int [] requests;
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
n = sc.nextInt();
d = sc.nextInt();
m = sc.nextInt();
requests = new int[m];
for(int i = 0; i < m; i++){
requests[i]=sc.nextInt();
}
Arrays.sort(requests);
//System.out.println(Arrays.toString(requests));
int left = 1;
int right = m;
while(left!=right){
int mid = left + (right-left)/2;
if(works(mid)){
right=mid;
}else{
left=mid+1;
}
}
System.out.println(left);
}
public static boolean works(int machines){
int [] timeArray = new int[m];
int time = 1;
timeArray[0]=1;
int currentMachines = machines-1;
for(int i = 1; i < m; i++){
if(requests[i]==requests[i-1]){
if(currentMachines==0){
currentMachines=machines-1;
time++;
timeArray[i]=time;
}else{
currentMachines--;
timeArray[i]=time;
}
}else{
time=Math.max(time+1, requests[i]);
timeArray[i]=time;
currentMachines=machines-1;
}
}
for(int i = 0; i < m; i++){
if(timeArray[i]-requests[i]>d){
return false;
}
}
return true;
}
}
