#include <bits/stdc++.h>   using namespace std;   int main() {     map<int, int> mp;     int n, k;     cin >> n >> k;     int c;     cin >> c;     for (int i = 1; i <= c; i++) {       int x;       cin >> x;       mp[x] = 1;     }     int ans = 0;     int t = 0;     for (int i = 1; i <= n; i++) {       t++;       if (mp[i] == 1) {         ans++;         t = 0;       } else if (t == k) {         ans++;         t = 0;       }     }     cout << ans << endl;     return 0;   }   