Problem:
Score : 600 points

Problem Statement

Snuke, a water strider, lives in a rectangular pond that can be seen as a grid with H east-west rows and W north-south columns. Let (i,j) be the square at the i-th row from the north and j-th column from the west.

Some of the squares have a lotus leaf on it and cannot be entered.
The square (i,j) has a lotus leaf on it if c_{ij} is @, and it does not if c_{ij} is ..

In one stroke, Snuke can move between 1 and K squares (inclusive) toward one of the four directions: north, east, south, and west.
The move may not pass through a square with a lotus leaf. Moving to such a square or out of the pond is also forbidden.

Find the minimum number of strokes Snuke takes to travel from the square (x_1,y_1) to (x_2,y_2).
If the travel from (x_1,y_1) to (x_2,y_2) is impossible, point out that fact.

Constraints

1 \leq H,W,K \leq 10^6

H \times W \leq 10^6

1 \leq x_1,x_2 \leq H

1 \leq y_1,y_2 \leq W

x_1 \neq x_2 or y_1 \neq y_2.

c_{i,j} is . or @.

c_{x_1,y_1} = .

c_{x_2,y_2} = .

All numbers in input are integers.

Input

Input is given from Standard Input in the following format:

H W K
x_1 y_1 x_2 y_2
c_{1,1}c_{1,2} .. c_{1,W}
c_{2,1}c_{2,2} .. c_{2,W}
:
c_{H,1}c_{H,2} .. c_{H,W}

Output

Print the minimum number of strokes Snuke takes to travel from the square (x_1,y_1) to (x_2,y_2), or print -1 if the travel is impossible.

Sample Input 1

3 5 2
3 2 3 4
.....
.@..@
..@..

Sample Output 1

5

Initially, Snuke is at the square (3,2).
He can reach the square (3, 4) by making five strokes as follows:

From (3, 2), go west one square to (3, 1).

From (3, 1), go north two squares to (1, 1).

From (1, 1), go east two squares to (1, 3).

From (1, 3), go east one square to (1, 4).

From (1, 4), go south two squares to (3, 4).

Sample Input 2

1 6 4
1 1 1 6
......

Sample Output 2

2

Sample Input 3

3 3 1
2 1 2 3
.@.
.@.
.@.

Sample Output 3

-1

Solution in Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

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

public class Main implements Runnable {
	boolean oj = true;
	Reader scn;
	PrintWriter out;
	String INPUT = "";

	void solve() {
		int n = scn.nextInt(), m = scn.nextInt(), k = scn.nextInt();

		int x = scn.nextInt() - 1, y = scn.nextInt() - 1;
		int dx = scn.nextInt() - 1, dy = scn.nextInt() - 1;

		boolean[][] arr = new boolean[n][m];
		for (int i = 0; i < n; i++) {
			String s = scn.next();
			for (int j = 0; j < n; j++) {
				if (s.charAt(j) == '@') {
					arr[i][j] = true;
				}
			}
		}

		int[][] dp = new int[n][m];
		scn.deepFillInt(dp, Integer.MAX_VALUE);
		dp[x][y] = 0;
		PriorityQueue<int[]> pq = new PriorityQueue<int[]>((o1, o2) -> o1[2] - o2[2]);
		pq.add(new int[] { x, y, 0 });

		int d = 0;
		while (!pq.isEmpty()) {
			int[] rv = pq.poll();
			x = rv[0];
			y = rv[1];
			d = rv[2];

			// left -> 0
			for (int j = y - 1; j >= 0; j--) {
				if (arr[x][j]) {
					break;
				}
				int steps = (y - j + k - 1) / k;
				if (dp[x][j] > d + steps) {
					dp[x][j] = d + steps;
					pq.add(new int[] { x, j, d + steps });
				} else {
					break;
				}
			}

			// right -> 1
			for (int j = y + 1; j < m; j++) {
				if (arr[x][j]) {
					break;
				}
				int steps = (j - y + k - 1) / k;
				if (dp[x][j] > d + steps) {
					dp[x][j] = d + steps;
					pq.add(new int[] { x, j, d + steps });
				} else {
					break;
				}
			}

			// up -> 2
			for (int i = x - 1; i >= 0; i--) {
				if (arr[i][y]) {
					break;
				}
				int steps = (x - i + k - 1) / k;
				if (dp[i][y] > d + steps) {
					dp[i][y] = d + steps;
					pq.add(new int[] { i, y, d + steps });
				} else {
					break;
				}
			}
			
			// down -> 3
			for (int i = x + 1; i < n; i++) {
				if (arr[i][y]) {
					break;
				}
				int steps = (i - x + k - 1) / k;
				if (dp[i][y] > d + steps) {
					dp[i][y] = d + steps;
					pq.add(new int[] { i, y, d + steps });
				} else {
					break;
				}
			}
		}
		if(dp[dx][dy] == Integer.MAX_VALUE) {
			dp[dx][dy] = -1;
		}
		out.println(dp[dx][dy]);
	}

	public void run() {
		long time = System.currentTimeMillis();
		boolean judge = System.getProperty("ONLINE_JUDGE") != null || oj;
		out = new PrintWriter(System.out);
		scn = new Reader(judge);
		solve();
		out.flush();
		if (!judge) {
			System.out.println(Arrays.deepToString(new Object[] { System.currentTimeMillis() - time + " ms" }));
		}
	}

	public static void main(String[] args) {
		new Thread(null, new Main(), "Main", 1 << 28).start();
	}

	class Reader {
		InputStream is;

		public Reader(boolean oj) {
			is = oj ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		}

		byte[] inbuf = new byte[1024];
		public int lenbuf = 0, ptrbuf = 0;

		int readByte() {
			if (lenbuf == -1)
				throw new InputMismatchException();
			if (ptrbuf >= lenbuf) {
				ptrbuf = 0;
				try {
					lenbuf = is.read(inbuf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (lenbuf <= 0)
					return -1;
			}
			return inbuf[ptrbuf++];
		}

		boolean isSpaceChar(int c) {
			return !(c >= 33 && c <= 126);
		}

		int skip() {
			int b;
			while ((b = readByte()) != -1 && isSpaceChar(b))
				;
			return b;
		}

		String next() {
			int b = skip();
			StringBuilder stringB = new StringBuilder();
			while (!(isSpaceChar(b))) { // when nextLine, (isSpaceChar(b) && b != ' ')
				stringB.appendCodePoint(b);
				b = readByte();
			}
			return stringB.toString();
		}

		String nextLine() {
			int b = skip();
			StringBuilder stringB = new StringBuilder();
			while ((!isSpaceChar(b) || b == ' ')) { // when nextLine, (isSpaceChar(b) && b != ' ')
				stringB.appendCodePoint(b);
				b = readByte();
			}
			return stringB.toString();
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		char nextChar() {
			return (char) skip();
		}

		char[] next(int n) {
			char[] buff = new char[n];
			int b = skip(), p = 0;
			while (p < n && !(isSpaceChar(b))) {
				buff[p++] = (char) b;
				b = readByte();
			}
			return n == p ? buff : Arrays.copyOf(buff, p);
		}

		int nextInt() {
			int num = 0, b;
			boolean minus = false;
			while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
				;
			if (b == '-') {
				minus = true;
				b = readByte();
			}

			while (true) {
				if (b >= '0' && b <= '9') {
					num = num * 10 + (b - '0');
				} else {
					return minus ? -num : num;
				}
				b = readByte();
			}
		}

		long nextLong() {
			long num = 0;
			int b;
			boolean minus = false;
			while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
				;
			if (b == '-') {
				minus = true;
				b = readByte();
			}

			while (true) {
				if (b >= '0' && b <= '9') {
					num = num * 10 + (b - '0');
				} else {
					return minus ? -num : num;
				}
				b = readByte();
			}
		}

		long[] nextLongArr(int n) {
			long[] a = new long[n];
			for (int i = 0; i < n; i++)
				a[i] = nextLong();
			return a;
		}

		int[] nextIntArr(int n) {
			int[] a = new int[n];
			for (int i = 0; i < n; i++)
				a[i] = nextInt();
			return a;
		}

		char[][] nextMat(int n, int m) {
			char[][] map = new char[n][];
			for (int i = 0; i < n; i++)
				map[i] = next(m);
			return map;
		}

		long[][] next2Long(int n, int m) {
			long[][] arr = new long[n][];
			for (int i = 0; i < n; i++) {
				arr[i] = nextLongArr(m);
			}
			return arr;
		}

		int[][] next2Int(int n, int m) {
			int[][] arr = new int[n][];
			for (int i = 0; i < n; i++) {
				arr[i] = nextIntArr(m);
			}
			return arr;
		}

		long[] shuffle(long[] arr) {
			Random r = new Random();
			for (int i = 1, j; i < arr.length; i++) {
				j = r.nextInt(i);
				arr[i] = arr[i] ^ arr[j];
				arr[j] = arr[i] ^ arr[j];
				arr[i] = arr[i] ^ arr[j];
			}
			return arr;
		}

		int[] shuffle(int[] arr) {
			Random r = new Random();
			for (int i = 1, j; i < arr.length; i++) {
				j = r.nextInt(i);
				arr[i] = arr[i] ^ arr[j];
				arr[j] = arr[i] ^ arr[j];
				arr[i] = arr[i] ^ arr[j];
			}
			return arr;
		}

		long[] uniq(long[] arr) {
			arr = scn.shuffle(arr);
			Arrays.parallelSort(arr);
			long[] rv = new long[arr.length];
			int pos = 0;
			rv[pos++] = arr[0];
			for (int i = 1; i < arr.length; i++) {
				if (arr[i] != arr[i - 1]) {
					rv[pos++] = arr[i];
				}
			}
			return Arrays.copyOf(rv, pos);
		}

		int[] uniq(int[] arr) {
			arr = scn.shuffle(arr);
			Arrays.parallelSort(arr);
			int[] rv = new int[arr.length];
			int pos = 0;
			rv[pos++] = arr[0];
			for (int i = 1; i < arr.length; i++) {
				if (arr[i] != arr[i - 1]) {
					rv[pos++] = arr[i];
				}
			}
			return Arrays.copyOf(rv, pos);
		}

		long[] reverse(long[] arr) {
			int i = 0, j = arr.length - 1;
			while (i < j) {
				arr[i] = arr[i] ^ arr[j];
				arr[j] = arr[i] ^ arr[j];
				arr[i] = arr[i] ^ arr[j];
				i++;
				j--;
			}
			return arr;
		}

		int[] reverse(int[] arr) {
			int i = 0, j = arr.length - 1;
			while (i < j) {
				arr[i] = arr[i] ^ arr[j];
				arr[j] = arr[i] ^ arr[j];
				arr[i] = arr[i] ^ arr[j];
				i++;
				j--;
			}
			return arr;
		}

		long[] compres(long[] arr) {
			int n = arr.length;
			long[] rv = Arrays.copyOf(arr, n);
			rv = uniq(rv);
			for (int i = 0; i < n; i++) {
				arr[i] = Arrays.binarySearch(rv, arr[i]);
			}
			return arr;
		}

		int[] compres(int[] arr) {
			int n = arr.length;
			int[] rv = Arrays.copyOf(arr, n);
			rv = uniq(rv);
			for (int i = 0; i < n; i++) {
				arr[i] = Arrays.binarySearch(rv, arr[i]);
			}
			return arr;
		}

		void deepFillLong(Object array, long val) {
			if (!array.getClass().isArray()) {
				throw new IllegalArgumentException();
			}
			if (array instanceof long[]) {
				long[] intArray = (long[]) array;
				Arrays.fill(intArray, val);
			} else {
				Object[] objArray = (Object[]) array;
				for (Object obj : objArray) {
					deepFillLong(obj, val);
				}
			}
		}

		void deepFillInt(Object array, int val) {
			if (!array.getClass().isArray()) {
				throw new IllegalArgumentException();
			}
			if (array instanceof int[]) {
				int[] intArray = (int[]) array;
				Arrays.fill(intArray, val);
			} else {
				Object[] objArray = (Object[]) array;
				for (Object obj : objArray) {
					deepFillInt(obj, val);
				}
			}
		}

		void tr(Object... o) {
			if (!oj)
				System.out.println(Arrays.deepToString(o));
		}
	}
}