9. Коровы - в стойла.

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

public class Main {
    public static void main(String args[]) {
        try (PrintWriter out = new PrintWriter(System.out)) {
            Scanner in = new Scanner(System.in);
            int n = in.nextInt();
            long k = in.nextLong();
            long max = -1;
            long sum = 0;
            long[] a = new long[n];
            a[0] = in.nextLong();

            for (int i = 1; i < n; i++) {
                a[i] = in.nextLong();
                sum += a[i] - a[i - 1];
            }

            long l = 1;
            long r = sum;

            while (l < r) {
                long m = (l + r) / 2;

                int ind = 1;
                long count = 1;
                boolean curFlag = true;
                while (ind < n && count < k) {
                    long curSum = 0;
                    while (ind < n && curSum < m) {
                        curSum += a[ind] - a[ind - 1];
                        ind++;
                    }
                    if (curSum < m)
                        curFlag = false;

                    count++;
                }
                if (count == k && curFlag) {
                    l = m + 1;
                    if (max < m)
                        max = m;
                } else r = m;
            }

            out.print(max);
        } catch(Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}