#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define pasha ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define int long long
#define ff first
#define ss second
#define pb push_back
#define all(v) begin(v), end(v)
using namespace std;
// mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
constexpr int N = 1e+5 + 5, oo = 2e+18;
void _() {
int n, d, m; cin >> n >> d >> m;
vector<int> a(m);
vector<int> f(n + 1, 0);
for (int i = 0; i < m; ++i) {
cin >> a[i];
++f[a[i]];
}
int lo = 1, hi = n, ans = n;
while (lo <= hi) {
int mid = (lo + hi) >> 1;
queue<int> q;
bool ok = true;
for (int i = 1; i <= n; ++i) {
int x = f[i];
while (x--) q.push(i);
if (!q.empty()) {
for (int j = 0; j < mid && !q.empty(); ++j) {
if (i >= q.front() + d) {
ok = false;
break;
}
q.pop();
}
if (!ok) break;
if (q.empty()) {
continue;
}
}
if (!ok) break;
}
if (ok) {
ans = mid;
hi = mid - 1;
} else {
lo = mid + 1;
}
}
cout << ans << '\n';
}
signed main() {
pasha
int t = 1;
// cin >> t;
for (int cs = 1; cs <= t; ++cs) {
_();
// cout << '\n';
}
}
