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

public class Solution {
	public static boolean check(long x, long[] cows, int N, int M, int C) {
		long first = cows[0];
		int used = 1;
		int cap = 0;

		// minimum buses needed to have maximum wait time = x
		for (int i = 0; i < N; i++) {
			if (cows[i] - first > x || cap >= C) {
				first = cows[i];
				used++;
				cap = 0;
			}
			cap++; // add cow to bus
		}

		return used <= M;
	}

	// find maximum waiting time
	public static long search(long[] cows, int N, int M, int C) {
		long max = 1_000_000_001;
		long pos = max;

		for (long x = max; x >= 1; x /= 2) {
			while (check(pos - x, cows, N, M, C)) {
				pos -= x;
			}
		}

		return pos;
	}

    public static void main(String[] args) throws Exception {
        FastScanner io = new FastScanner("convention"); // usaco submission file
		// FastScanner io = new FastScanner();

		int N = io.nextInt(), M = io.nextInt(), C = io.nextInt();
		long[] cows = new long[N];
		for (int i = 0; i < N; i++) { cows[i] = io.nextLong(); }
		
		Arrays.sort(cows);

		long answer = search(cows, N, M, C);
		io.println(answer);

		io.close();
    }

    /**
        SPECIAL NUMBERS
    */
    public static int MOD = 1_000_000_007;

    /**
        DATA STRUCTURES
    */
    static class MultiSet {
        static TreeMap<Integer, Integer> multiset = new TreeMap<>();
        static void add(int x) {
            multiset.putIfAbsent(x, 0);
            multiset.put(x, multiset.get(x)+1);
        }
        static void remove(int x) {
            multiset.putIfAbsent(x, 0);
            multiset.put(x, multiset.get(x)-1);
            if (multiset.get(x) <= 0) multiset.remove(x);
        }
    }

    /**
        IO
    */
    static class FastScanner extends PrintWriter {
        private BufferedReader br;
        private StringTokenizer st;
		
		// standard input
        public FastScanner() { this(System.in, System.out); }
		public FastScanner(InputStream i, OutputStream o) {
            super(o);
			st = new StringTokenizer("");
            br = new BufferedReader(new InputStreamReader(i));
        }
		// USACO-style file input
        public FastScanner(String problemName) throws IOException {
            super(problemName + ".out");
			st = new StringTokenizer("");
            br = new BufferedReader(new FileReader(problemName + ".in"));
        }

        // returns null if no more input
        public String next() {
            try {
                while (st == null || !st.hasMoreTokens())
                    st = new StringTokenizer(br.readLine());
                return st.nextToken();
            } catch (Exception e) { }
            return null;
        }
        public int nextInt() { return Integer.parseInt(next()); }  
        public double nextDouble() { return Double.parseDouble(next()); }   
        public long nextLong() { return Long.parseLong(next()); }   
    }
}