#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <queue>
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, d, m;
cin >> n >> d >> m;
vector <pair <int, int>> reg(m + 1);
for (int i = 1;i <= m;i++) {
cin >> reg[i].first;
reg[i].second = i;
}
sort(reg.begin(), reg.end());
int l = 1, r = 1e9;
while (l + 1 < r) {
int mid = (l + r) / 2;
bool pos = true;
int day = 1;
for (int i = 1;i <= m;) {
int cnt = mid;
while (cnt && i <= m) {
if (reg[i].first > day) break;
if (reg[i].first + d < day) {
pos = false;
break;
}
i++;
cnt--;
}
day++;
}
if (pos) {
r = mid;
}
else {
l = mid;
}
}
cout << r << endl;
return 0;
}
