#include <bits/stdc++.h>
#define int long long
int n,d,m;
int jobs[100010];
bool solve(int amt){
std::queue<std::pair<int,int>> q;
for(int i=1;i<=n;i++){
//std::cout << amt << ' ' << i << '\n';
if(jobs[i]!=0)
q.push({i,jobs[i]});
int left = amt;
if(!q.empty()&&i-d>q.front().first)return false;
while(!q.empty()&&q.front().second<=left)left-=q.front().second,q.pop();
if(!q.empty()&&q.front().second>left)q.front().second-=left;
}
return true;
}
signed main(){
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cin >> n >> d >> m;
for(int i=0;i<m;i++){
int day;
std::cin >> day;
jobs[day]+=1;
}
int l=0,r=m;
while(l<r){
int mid = (l+r)/2;
if(solve(mid)){
r=mid;
}
else{
l=mid+1;
}
}
std::cout << r;
}
