#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <map>
#include <set>
#include <climits>
#include <cmath>
#include <fstream>
#include <queue>
using namespace std;
int main() {
int n, d, m;
cin >> n >> d >> m;
vector<int> nums(n);
for (int i = 0; i < m; i++) {
int temp;
cin >> temp;
temp--;
nums[temp]++;
}
int lo = 0;
int hi = 1000005;
while (lo < hi) {
int mid = (lo + hi) / 2;
int counterCows = 0;
for (int i = 0; i < n - d; i++) {
counterCows += nums[i];
counterCows = max(counterCows - mid, 0);
}
if (counterCows == 0) {
hi = mid;
}
else {
lo = mid + 1;
}
}
cout << hi << endl;
}
