// https://oj.uz/problem/view/CEOI12_jobs
#include <bits/stdc++.h>
using namespace std;
int main() {
int N, D, M;
cin >> N >> D >> M;
vector<int> requests;
requests.resize(M);
for (int i = 0; i < M; i++) {
cin >> requests[i];
}
sort(requests.begin(), requests.end());
int left = 1, right = M;
while (left < right) {
int mid = (left + right) / 2;
// cout<<mid<<endl;
// 1 2 4 2 1 3 5 6 2 3 6 4
// 1,1,2,2,2,3,3,4,4,5,6,6
int index = 0;
bool enough = true;
for (int i = 1; i <= N; i++) {
if (index >= M) {
break;
}
for (int j = 0; j < mid; j++) {
if (index >= M) {
break;
}
if (requests[index] > i + D) {
enough = false;
break;
}
if (requests[index] > i) {
break;
}
index++;
}
if (enough == false) {
break;
}
}
if(index<M-1){
enough=false;
}
if (enough == true) {
right = mid;
} else {
left = mid + 1;
}
}
cout << left;
return 0;
}
