#include <bits/stdc++.h>
#define int long long
using namespace std;
// return true if can use count no. of machines to handle all jobs
bool ok(int count, int n, int d, int m, vector<array<int, 2>>& jobs) {
queue<int> q;
for (int i = 1, j = 0; i <= n; i++) {
while (j < m && jobs[j][0] == i) {
q.push(j++);
}
if (q.size() && i - jobs[q.front()][0] > d) return false;
for (int rep = 0; rep < count && !q.empty(); rep++) {
q.pop();
}
}
return true;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, d, m;
cin >> n >> d >> m;
vector<array<int, 2>> jobs(m);
for (int i = 0; i < m; i++) {
cin >> jobs[i][0];
jobs[i][1] = i + 1;
}
sort(jobs.begin(), jobs.end());
int lo = 1, hi = m, ans = m;
while (lo <= hi) {
int mid = lo + (hi - lo) / 2;
if (ok(mid, n, d, m, jobs)) {
ans = mid;
hi = mid - 1;
} else {
lo = mid + 1;
}
}
cout << ans << endl;
}
