import java.util.*;
import java.io.*;
import java.text.*;

public class NickyEnMark{
    public static void main(String[] args) throws IOException {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int k = scanner.nextInt();
        int[] a = new int[n];
        int[] ap = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = scanner.nextInt();
            ap[i] = a[i];
        }

        Arrays.sort(ap);

        int ans = 0;
        for (int i = 0; i < n; i++) {
            for (int j = i; j >= 0; j--) {
                if (ap[j] == a[i]) {
                    int d = Math.abs(j - i);
                    ans = Math.max(ans, d);
                    break;
                }
            }
        }

        int realAns = (int)Math.ceil(ans * 1.0 / (k - 1));
        System.out.println(realAns);
    }
}