#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
const uint64_t SEED = chrono::high_resolution_clock::now().time_since_epoch().count();
struct chash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
return splitmix64(x + SEED);
}
};
#define int int64_t
constexpr int INF = INT64_MAX;
int32_t main() {
cin.tie(nullptr);
ios_base::sync_with_stdio(false);
int n,d,m;
cin>> n >> d >> m;
vector<int> days(n);
for (int i = 0; i < m; i++) {
int m_i; cin >> m_i;
m_i--;
days[m_i]++;
days[m_i + d]--;
}
int max_concurrent = -INF;
int cur = 0;
for (int i = 0; i < n; i++) {
cur += days[i];
max_concurrent = max(max_concurrent,cur);
}
cout << max_concurrent / d << '\n';
}
