#include <bits/stdc++.h>
using namespace std;
int n, d, m;
vector<pair<int,int> > v;
vector<vector<int> > rez;
bool ok(int masini) {
int den=1;
vector<vector<int> > raspored(n+1);
for (int i=0;i<m;i+=masini) {
for (int j=i;j<i+masini;j++) {
while (v[j].first>den)
den++;
if (v[j].first+d<den)
return false;
raspored[den].push_back(v[j].second);
}
den++;
}
rez.clear();
rez=raspored;
return true;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cin >> n >> d >> m;
v.resize(m);
for (int i=0;i<m;i++) {
cin >> v[i].first;
v[i].second=i+1;
}
sort(v.begin(), v.end());
int l=0, r=m;
while (l+1<r) {
int mid=(l+r)/2;
if (ok(mid)) r=mid;
else l=mid;
}
cout << r << '\n';
/*for (int i=1;i<rez.size();i++) {
for (auto x:rez[i])
cout << x << " ";
cout << "0" << '\n';
}*/
return 0;
}
