/*
_ __ __ __ ____ ___ _ __
| | /| / / ___ _ / /_ ____ / / / __ \ ___ ___ / _ \ (_) ___ ____ ___ / /
| |/ |/ / / _ `// __// __/ / _ \ / /_/ / / _ \/ -_) / ___/ / / / -_)/ __// -_) /_/
|__/|__/ \_,_/ \__/ \__/ /_//_/ \____/ /_//_/\__/ /_/ /_/ \__/ \__/ \__/ (_)
*/
#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
// #pragma GCC target("avx2")
#include <bits/stdc++.h>
#define ll long long
#define ull unsigned ll
#define ld long double
#define all(v) v.begin(), v.end()
#define allr(v, l, r) v.begin() + l, v.begin() + r + 1
#define rall(v) v.rbegin(), v.rend()
#define rallr(v, l, r) v.rbegin() + ((int)v.size() - 1 - r), v.rbegin() + ((int)v.size() - l)
#define endl "\n"
#define newline cout << endl;
using namespace std;
// constants
const int INF = 1e9;
// functions
// structs
// globals
// notes
/*
-stuff you should look for-
* int overflow, array bounds
* special cases (n=1?)
* do something instead of nothing and stay organized
* WRITE STUFF DOWN
* DON'T GET STUCK ON ONE APPROACH
continue - skip the rest in the loop
*/
void solve()
{
int n, D, m;
cin >> m >> D >> n;
vector <int> a(m + 1, 0);
for (int i = 1; i <= n; i++)
{
int x;
cin >> x;
a[x]++;
}
auto check = [&](int machines) -> bool
{
queue <int> q;
for (int i = 1; i <= m; i++)
{
int left = machines;
while (!q.empty())
{
if (q.front() + D < i)
{
return false;
}
if (left)
{
q.pop();
left--;
}
}
int x = max(0, a[i] - left);
while (x)
{
q.push(i);
x--;
}
}
return q.empty();
};
int L = 1, R = n;
while (L <= R)
{
int mid = (L + R) / 2;
if (check(mid))
{
R = mid - 1;
}
else
{
L = mid + 1;
}
}
cout << L;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
int testcount = 1;
// cin >> testcount;
while (testcount--)
{
solve();
newline
}
}
/*
$$$$$$$$\ $$$$$$$$\
$$ _____|\____$$ |
$$ | $$ /
$$$$$\ $$ /
$$ __| $$ /
$$ | $$ /
$$$$$$$$\ $$$$$$$$\
\________|\________|
*/
