#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  if ((n - k) % (k - 1) == 0)
    cout << ((n - k) / (k - 1)) + 1 << endl;
  else
    cout << ((n - k) / (k - 1)) + 2 << endl;
  return 0;
}
