#include "bits/stdc++.h"
using namespace std;
const int N = 1e5 + 1;
int n, d, m;
pair<int, int> a[N];
bool good(int k) {
int j = 1;
for (int i = 1; i <= n; ++i) {
for (int x = 1; x <= k; ++x) {
if (a[j].first > i) break;
if (a[j].first + d < i) return false;
if (j == m) return true;
++j;
}
}
return false;
}
int32_t main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n >> d >> m;
for (int i = 1; i <= m; ++i) {
cin >> a[i].first;
a[i].second = i;
}
sort(a + 1, a + 1 + m);
int l = 0, r = m + 1;
while (r - l > 1) {
int mid = (l + r) >> 1;
if (good(mid)) r = mid;
else l = mid;
}
cout << r << '\n';
}
