Problem: Consider a grid with H rows and W columns of squares. Let (r, c) denote the square at the r-th row from the top and the c-th column from the left. Each square is painted black or white.

The grid is said to be good if and only if the following condition is satisfied:

* From (1, 1), we can reach (H, W) by moving one square right or down repeatedly, while always being on a white square.



Note that (1, 1) and (H, W) must be white if the grid is good.

Your task is to make the grid good by repeating the operation below. Find the minimum number of operations needed to complete the task. It can be proved that you can always complete the task in a finite number of operations.

* Choose four integers r_0, c_0, r_1, c_1(1 \leq r_0 \leq r_1 \leq H, 1 \leq c_0 \leq c_1 \leq W). For each pair r, c (r_0 \leq r \leq r_1, c_0 \leq c \leq c_1), invert the color of (r, c) - that is, from white to black and vice versa.

Constraints

* 2 \leq H, W \leq 100

Input

Input is given from Standard Input in the following format:


H W
s_{11} s_{12} \cdots s_{1W}
s_{21} s_{22} \cdots s_{2W}
\vdots
s_{H1} s_{H2} \cdots s_{HW}


Here s_{rc} represents the color of (r, c) - `#` stands for black, and `.` stands for white.

Output

Print the minimum number of operations needed.

Examples

Input

3 3
.##
.#.
##.


Output

1


Input

3 3
.##
.#.
.


Output

1


Input

2 2
.
.#


Output

2


Input

4 4
..##
...
.
.


Output

0


Input

5 5
.#.#.
.#.#
.#.#.
.#.#
.#.#.


Output

4

Solution (in JAVA):

Solution:
import java.util.*;
import java.util.stream.Collectors;
import java.io.*;
import java.math.BigDecimal;
import java.nio.charset.StandardCharsets;

public class Main {
	int H, W;
	int[][] distances;
	boolean[][] field;

	public static void main(String[] args) throws IOException {
		InputStreamReader reader = new InputStreamReader(System.in, StandardCharsets.UTF_8);
		BufferedReader in = new BufferedReader(reader);
		Main ins = new Main(in);
		ins.calc();
		ins.showResult();
	}

	Main(BufferedReader in) throws IOException {
		String[] tokens = in.readLine().split(" ");
		H = Integer.parseInt(tokens[0]);
		W = Integer.parseInt(tokens[1]);
		this.distances = new int[H][W];
		this.field = new boolean[H][W];
		for (int i = 0; i < H; ++i) {
			Arrays.fill(this.distances[i], 0);
			Arrays.fill(this.field[i], true);
		}
		for (int i = 0; i < H; ++i) {
			String line = in.readLine();
			for (int j = 0; j < W; ++j) {
				char c = line.charAt(j);
				if (c == '.') {
					this.field[i][j] = true;
				} else {
					this.field[i][j] = false;
				}
			}
		}
		if (!this.field[0][0]) {
			this.distances[0][0] = 1;
		}
		// 横
		for (int i = 1; i < W; ++i) {
			if (this.field[0][i]) {
				// 白
				this.distances[0][i] = this.distances[0][i - 1];
			} else {
				// 黒
				// もし前のものが黒なら，そのまま行ける
				if (!this.field[0][i - 1]) {
					this.distances[0][i] = this.distances[0][i - 1];
				} else {
					this.distances[0][i] = this.distances[0][i - 1] + 1;
				}
			}
		}
		// 縦
		for (int i = 1; i < H; ++i) {
			if (this.field[i][0]) {
				// 白
				this.distances[i][0] = this.distances[i - 1][0];
			} else {
				// 黒
				// もし前のものが黒なら，そのまま行ける
				if (!this.field[i - 1][0]) {
					this.distances[i][0] = this.distances[i - 1][0];
				} else {
					this.distances[i][0] = this.distances[i - 1][0] + 1;
				}
			}
		}
	}

	void calc() {
		for (int i = 1; i < H; ++i) {
			for (int j = 1; j < W; ++j) {
				boolean cond = this.field[i][j];
				if (cond) {
					// 現在位置は白
					this.distances[i][j] = Math.min(this.distances[i - 1][j], this.distances[i][j - 1]);
				} else {
					// 現在位置は黒
					if (this.field[i - 1][j] && this.field[i][j - 1]) {
						// 両方白
						this.distances[i][j] = Math.min(this.distances[i - 1][j] + 1, this.distances[i][j - 1] + 1);
					} else if (this.field[i - 1][j] && !this.field[i][j - 1]) {
						// 左が黒
						this.distances[i][j] = Math.min(this.distances[i - 1][j] + 1, this.distances[i][j - 1]);
					} else if (!this.field[i - 1][j] && this.field[i][j - 1]) {
						// 上が黒
						this.distances[i][j] = Math.min(this.distances[i - 1][j], this.distances[i][j - 1] + 1);
					} else {
						// 左，うえが黒
						this.distances[i][j] = Math.min(this.distances[i - 1][j], this.distances[i][j - 1]);
					}
				}
			}
		}
	}

	void showResult() {
		// 開始位置が黒の場合は++1しないといけない
		int result = this.distances[H - 1][W - 1];
		System.out.println(result);
	}

}