#pragma GCC optimize "-O3"
#pragma GCC optimize("Ofast")
#pragma GCC optimization ("unroll-loops")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#define NumberOfOnes __builtin_popcount
#define LSOne(S) (S & (-S))
#define ll long long
#define two pair<int,int>
#define twoll pair<ll,ll>
#define four pair<two,two>
#define pb push_back
#define eb emplace_back
#define mk make_pair
#define y1 y1922
#define INF 1000000000000000000
#define P 1000000007
#define lmax 1000000000
#define nn 1000003
#define ff first.first
#define fs first.second
#define sf second.first
#define ss second.second
#define f first
#define s second
#define vi vector<int>
#define vll vector<ll>
#define vtwo vector<two>
#define ALL(container) (container).begin(), (container).end()
#define sz(container) (int)(container.size())
#define max(a,b) ((a)>(b)?(a):(b))
#define min(a,b) ((a)<(b)?(a):(b))
#define mid(a,b) (a+b>>1)
#define minN 0
#define maxN 10000000
#define na(x) ((x)<P?(x):(x)-P)
#define ab(a) (-(a)<(a)?(a):-(a))
#define FAST std::ios::sync_with_stdio(false)
#define xRand mt19937 rng(chrono::steady_clock::now().time_since_epoch().count())
#define rnd rng
#define IT iterator
typedef
tree<
int,// aq pair<int,int> shegidzlia
null_type,
less/*_equal*/<int>,// aqac
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
// '_equal' mashin ginda roca multiset gchirdeba
template<class key, class value,class cmp = std::less<key>>
using ordered_map = tree<key, value, cmp, rb_tree_tag, tree_order_statistics_node_update>;
ordered_map<int, int> my_map;
inline int rin(){
int x=0,w=1;char ch=getchar();
while ((ch<'0'||ch>'9')&&ch!='-') ch=getchar();
if (ch=='-') w=0,ch=getchar();
while (ch>='0'&&ch<='9') x=(x<<3)+(x<<1)+ch-'0',ch=getchar();
return w?x:-x;
}
inline int bin(){
int x=0;char ch=getchar();
while (ch<'0'||ch>'9') ch=getchar();
while (ch>='0'&&ch<='9') x=(x<<3)+(x<<1)+ch-'0',ch=getchar();
return x;
}
int n,m,k;
two a[100004];
bool che(int g){
int u=1,o=0;
while(u<k){
int d=g;
o++;
while(d--&&u<k){
if(a[u].f+m<o) return 0;
u++;
}
if(u>k) return 1;
}
return 1;
}
int main(){FAST;xRand;
cin>>n>>m>>k;
for(int i=1;i<=k;i++){
cin>>a[i].f;
a[i].s=i;
}
sort(a+1,a+1+k);
int l=1,r=k;
while(l<r){
int md=mid(l,r);
if(che(md)){
r=md;
}else{
l=md+1;
}
}
if(che(l-1)) l--;
cout<<l<<endl;
}
/*
* *
* * * *
* * * *
* * * *
* * * * *
* * * *
* * * *
* * *
* *
*/
