#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pll pair<int, int>
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define endl '\n'
signed main(){
int n,d,m;cin>>n>>d>>m;
vector<vector<int>> v(n+1);
for(int i=1;i<=m;i++){
int d;cin>>d;
v[d].pb(i);
}
int l=0, r=1000000,mac;
while(r-l>1){
mac=(l+r)/2;
vector<int> use(n+1, 0), rem(n+1,0);
for(int i=1;i<=n;i++)rem[i]=v[i].size();
int usep=0;
bool ok=true;
for(int i=1;i<=n;i++){
usep=max(usep, i);
while(rem[i] and usep<=i+d){
int take=min(rem[i], mac-use[usep]);
use[usep]+=take;
rem[i]-=take;
if(use[usep]==mac)usep++;
}
if(rem[i] and usep > i+d){
ok=false;
break;
}
}
//~ printf("with %lld machines, use is \n", mac);
//~ for(int i=1;i<=n;i++){
//~ cout<<use[i]<<" ";
//~ }
//~ cout<<endl;
if(ok){
r=mac;
}
else l=mac;
}
cout<<r<<"\n";
//~ vector<vector<int>> ans(n+1);
//~ int usep=
//~ for(int i=1;i<=n;i++){
//~ while(v[i].size() >= 0){
//~ ans[
}
