#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define endl "\n"
#define ll long long
#define mp make_pair
#define ins insert
#define lb lower_bound
#define pb push_back
#define ub upper_bound
#define lll __int128
#define fi first
#define se second
using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_multiset;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
int main() {
ios_base::sync_with_stdio(0); cin.tie(NULL);
int n, d, m;
cin >> n >> d >> m;
int a[m + 1];
for(int i = 1; i <= m; ++i)
cin >> a[i];
sort(a + 1, a + n + 1);
int cnt[n + 1];
memset(cnt, 0, sizeof(cnt));
for(int i = 1; i <= m; ++i)
++cnt[a[i]];
int l = 0, r = 1e6, ans = -1;
while(l <= r) {
int mid = (l + r) / 2;
int pend = 0;
for(int i = 1; i <= n; ++i) {
pend += cnt[i];
pend -= mid;
pend = max(pend, 0);
}
if(pend == 0) {
r = mid - 1, ans = mid;
}
else
l = mid + 1;
}
cout << ans << endl;
return 0;
}
