#include <bits/stdc++.h>
#define f first
#define s second
using namespace std;
const int N = 1e6 + 69;
int n, d, m, a[N], b[N];
vector<int> g[N];
signed main() {
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int tt = 1;
//cin >> tt;
while (tt--) {
cin >> n >> d >> m;
vector<int> c;
c.push_back(0);
for (int i = 1;i <= m;i++) {
cin >> a[i];
g[a[i]].push_back(i);
c.push_back(a[i]);
}
sort(c.begin(), c.end());
int l = 1, r = m, ans = 0;
auto check = [&](int mid) {
int t = 0;
for (int i = 1;i <= m;i++)
b[i] = (i + mid - 1) / mid;
for (int i = 1;i <= m;i++) {
t += 1;
if (t > mid) {
b[i] = b[i - 1] + 1;
t = 1;
}
if (b[i] < c[i]) {
b[i] = c[i];
t = 1;
}
}
for (int i = 1;i <= m;i++) {
if (c[i] + d < b[i])
return false;
}
return true;
};
while (l <= r) {
int mid = (l + r) / 2;
if (check(mid)) {
ans = mid;
r = mid - 1;
}
else
l = mid + 1;
}
cout << ans << '\n';
}
return 0;
}
