#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
pair<bool, vector<vector<int>>> calc(int n, int d, int x, vector<pair<int, int>> &brr, int m)
{
int j = 0;
bool p = true;
vector<vector<int>> temp(n);
for (int i = 0; i < n; i++)
{
int y = x;
while (y-- && j < m)
{
if (!(i + 1 <= brr[j].first + d))
{
p = false;
break;
}
temp[i].push_back(brr[j].second);
// cout << "day " << i + 1 << " processed " << j + 1 << " \n";
j++;
}
if (!p)
break;
}
return {p, temp};
}
void solve()
{
int n, d, m;
cin >> n >> d >> m;
vector<pair<int, int>> brr;
for (int i = 0; i < m; i++)
{
int x;
cin >> x;
brr.push_back({x, i + 1});
}
sort(brr.begin(), brr.end());
int l = 1, r = 1e6, ans = 1e6;
vector<vector<int>> ansvec;
while (l <= r)
{
int mid = (l + r) / 2;
pair<bool, vector<vector<int>>> temp = calc(n, d, mid, brr, m);
if (temp.first)
{
ans = mid;
ansvec = temp.second;
r = mid - 1;
}
else
{
l = mid + 1;
}
}
cout << ans << "\n";
// for (auto &i : ansvec)
// {
// if (!i.empty())
// {
// for (auto &j : i)
// cout << j << " ";
// }
// cout << 0 << "\n";
// }
}
// void setIO(string s)
// {
// freopen((s + ".in").c_str(), "r", stdin);
// freopen((s + ".out").c_str(), "w", stdout);
// }
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
solve();
return 0;
}
