#include <bits/stdc++.h>
using namespace std;
/*
ID: 10002181
LANG: C++
TASK: ariprog
*/
using str = string; // yay python!
using ld = long double; // or double, if TL is tight
using ll = long long;
using int64 = ll;
using db = double;
using ull = unsigned long long;
#define ch() getchar()
#define pc(x) putchar(x)
#define tcT template<class T
#define tcTU tcT, class U
tcT> using V = vector<T>;
tcT, size_t SZ> using AR = array<T,SZ>;
using vi = V<int>;
using vb = V<bool>;
using vpi = V<pair<int,int>>;
using vvi = V<vi>;
using vl = V<ll>;
using vd = V<ld>;
using vstr = V<str>;
#define mp make_pair
#define pi pair <int, int>
#define all(x) begin(x), end(x)
#define sor(x) sort(all(x))
#define rev(x) reverse(all(x))
#define sz(x) (int)(x).size()
#define AR array
#define F0R(i, a, b) for (int i=a; i<b;++i)
#define FOR(i, a) for (int i=0; i<a;++i)
#define FORn(i, a) for (int i=1; i<=a;++i)
#define ROF(i,a) for(int i=a-1; i >= 0;--i)
#define R0F(i,a,b) for(int i=a; i > b;--i)
#define ROFn(i,a) for(int i=a; i > 0;--i)
#define trav(i,x) for(auto& i:x)
// pairs
#define mp make_pair
#define f first
#define s second
// vectors
#define lb lower_bound
#define ub upper_bound
#define SUM(v) accumulate(all(v), 0LL)
#define MN(v) *min_element(all(v))
#define MX(v) *max_element(all(v))
#define eb emplace_back
#define ft front()
#define bk back()
#define ins insert
#define pf push_front
#define pb push_back
#define emt empty()
#define rsz resize
#define pob pop_back()
#define pof pop_front()
#define swp(a,b) a^=b^=a^=b
#define ts to_string
#define setIO() ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
const ll MOD = 1e9+7;
const ll MAX = 100000000000;
const ll INF = 1e18; // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
#ifdef _DEBUG
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1}; // for every grid problem!!
//INPUT
#define tcTUU tcT, class ...U
tcT> void re(complex<T>& c);
tcTU> void re(pair<T,U>& p);
tcT> void re(V<T>& v);
tcT, size_t SZ> void re(AR<T,SZ>& a);
tcT> void re(T& x) { cin >> x; }
void re(db& d) { str t; re(t); d = stod(t); }
void re(ld& d) { str t; re(t); d = stold(t); }
tcTUU> void re(T& t, U&... u) { re(t); re(u...); }
tcT> void re(complex<T>& c) { T a,b; re(a,b); c = {a,b}; }
tcTU> void re(pair<T,U>& p) { re(p.f,p.s); }
tcT> void re(V<T>& x) { trav(a,x) re(a); }
tcT> void rv(int n, V<T>& x) { x.rsz(n); re(x); }
//OUTPUT
tcT> void pr(V<T>& x) { FOR(i,sz(x)) cout << x[i] << " \n"[i + 1 == sz(x)];}
tcT> void pr(T x) { cout << ts(x); }
tcT> void ps() { cout << '\n'; }
void setF(string fileName = "") {
ios_base::sync_with_stdio(0); cin.tie(0);
if((int)fileName.size()) {
freopen((fileName+".in").c_str(), "r", stdin);
freopen((fileName+".out").c_str(), "w", stdout);
}
}
struct DSU {
vector<int> e;
DSU(int N) { e = vector<int>(N, -1); }
int get(int x) { return e[x] < 0 ? x : e[x] = get(e[x]); }
bool same_set(int a, int b) { return get(a) == get(b); }
int size(int x) { return -e[get(x)]; }
bool unite(int x, int y) { // union by size
x = get(x), y = get(y);
if (x == y) return false;
if (e[x] > e[y]) swap(x, y);
e[x] += e[y]; e[y] = x;
return true;
}
};
struct edge{
int a;
int b;
int w;
};
ll bpow(ll x, ll y){
x %= MOD;
ll res = 1LL;
while(y){
if (y & 1LL)
res *= x;
res %= MOD;
x = (x*x) % MOD;
y >>= 1LL;
}
return res;
}
ll gauss(int n){ return n*(n+1)/2; }
ll fact(int x){if(x) return x * (x - 1); return 1;}
/*
scanf("%lld", &testInteger);
printf("%lld", testInteger);
____ ____ ____ ____ ____ ____
||f |||l |||o |||p |||p ||||y ||
||__|||__|||__|||__|||__||||__||
|/__\|/__\|/__\|/__\|/__\||/__\|
**/
void solve(){
int N,D,M; cin >> N >> D >> M;
vpi A(M); FOR(i,M) { cin >> A[i].f; A[i].s = i; }
sor(A);
auto work = [&] (int x){
queue<int> q;
FOR(i,M){
//cout << sz(q) << ' ' << A[i].f << '\n';
if(sz(q) && A[i].f - q.ft > D) return false;
if(sz(q)) FOR(j,min((A[i].f - q.bk - 1) * x,sz(q))) q.pop();
q.push(A[i].f);
while(i + 1 < M && A[i + 1].f == A[i].f) { q.push(A[i].f); ++i; }
FOR(j,min(x,sz(q))) q.pop();
}
F0R(i,A[M - 1].f + 1,N){
if(sz(q) && A[i].f - q.ft > D) return false;
FOR(j,min(sz(q),x)) q.pop();
}
return true;
};
int l = 0,r = M + 1;
while(l < r - 1){
int mid = l + (r - l) / 2;
if(work(mid)) r = mid;
else l = mid;
}
cout << r << '\n';
}
// D - delay max
// 8 2 12
// 1 2 4 2 1 3 5 6 2 3 6 4
main()
{ // setIO();
solve();
}
//is y a vowel? Damian:1
// <3 :L ._. <_<
//You have no idea how high I can fly
