// Author : Jad Isaac
// ID: jadDebugs
// TASK: -----
// LANG: C++
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define f first
#define s second
#define pii pair<int, int>
int n, d, m;
bool works(int robots, vector<pii> jobs)
{
int endT[robots] = {0};
int maxD = 0;
for (int i = 0, cur = 0; i < m; i++, cur++) {
if (cur == robots)
cur = 0;
// if our end time for this job is > than our start time for this job
// there will be delay
if (endT[cur] + 1 > jobs[i].f) {
endT[cur]++;
maxD = max(maxD, endT[cur] - jobs[i].f);
}
else
endT[cur] = jobs[i].f;
}
return maxD <= d;
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n >> d >> m;
// first = day of req
// second = id or req
vector<pii> jobs(m);
for (int i = 0; i < m; i++) {
cin >> jobs[i].f;
jobs[i].s = i+1;
}
sort(begin(jobs), end(jobs));
int l = 0, r = m;
while (l < r) {
int mid = l + (r-l)/2;
if (works(mid, jobs))
r = mid;
else
l = mid+1;
}
cout << l << '\n';
return 0;
}
