#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 7;
int n, d, m;
int f[N];
bool check(int t) {
deque < pair <int, int> > h;
for(int i = 1; i <= n; i++) {
h.emplace_back(i, f[i]);
if(!h.empty()) {
h[0].second -= min(h[0].second, t);
int cur_t = t;
if(!h.empty() && cur_t) {
if(i - h[0].first > d) return false;
int next_t = cur_t;
next_t -= min(h[0].second, cur_t);
h[0].second -= min(h[0].second, cur_t);
cur_t = next_t;
if(h[0].second == 0) {
h.pop_back();
}
}
}
}
if(h.size()) return false;
return true;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> d >> m;
for(int i = 0; i < m; i++) {
int x;
cin >> x;
f[x]++;
}
int low = 1, high = n, best = n;
while(low <= high) {
int mid = (low + high) >> 1;
if(check(mid)) {
best = mid;
high = mid - 1;
} else {
low = mid + 1;
}
}
cout << best << '\n';
return 0;
}
