#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define For(i, a, b) for(int i=a; i<b; i++)
#define ffi For(i, 0, N)
#define ffj For(j, 0, M)
#define ffa ffi ffj
#define s <<" "<<
#define w cout
#define e "\n"
#define pb push_back
#define mp make_pair
#define a first
#define b second
//#define int ll
const int MAXN=1000000;//, INF=1000000000000000000;
///500,000,000
int D, N, inp[MAXN];
bool works(int m) {
int day = 1;
int lef = m;
ffi {
if (inp[i] > day) day=inp[i], lef = m;
if (inp[i] + D < day) return false;
lef--;
if (lef == 0) day++, lef=m;
}
return true;
}
int main() {
//ifstream cin("test.in");
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> N >> D >> N;
ffi cin >> inp[i];
sort(inp, inp+N);
int a=1, b=N;
while (a != b) {
int mid = (a+b)/2;
if (works(mid)) b = mid;
else a = mid+1;
}
w<< a<<e;
}
