using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace AtCorder
{
	public class Program
	{
		static void Main(string[] args)
		{
			var cin = new Scanner2();
			int h = cin.Int();
			int w = cin.Int();
			var s = new string[h];
			for (int i = 0; i < h; i++) {
				s[i] = cin.Next();
			}

			var d = new int[h, w];
			for (int i = 0; i < h; i++) {
				for (int j = 0; j < w; j++) {
					d[i, j] = int.MaxValue;
				}
			}

			d[0, 0] = 0;
			var q = new Queue<Position>();
			q.Enqueue(new Position {
				X = 0,
				Y = 0,
				D = s[0][0] == '#' ? 1 : 0,
				IsBlack = s[0][0] == '#' });
			while (q.Count > 0) {
				var cur = q.Dequeue();
				if (cur.X < w - 1) {
					int nd = 0;
					if (cur.IsBlack) {
						nd = cur.D;
					} else {
						if (s[cur.Y][cur.X + 1] == '#') {
							nd = cur.D + 1;
						} else {
							nd = cur.D;
						}
					}

					if (d[cur.Y, cur.X + 1] > nd) {
						d[cur.Y, cur.X + 1] = nd;
						q.Enqueue(new Position { 
							X = cur.X + 1,
							Y = cur.Y,
							D = nd,
							IsBlack = s[cur.Y][cur.X + 1] == '#' });
					}
				}

				if (cur.Y < h - 1) {
					int nd = 0;
					if (cur.IsBlack) {
						nd = cur.D;
					} else {
						if (s[cur.Y + 1][cur.X] == '#') {
							nd = cur.D + 1;
						} else {
							nd = cur.D;
						}
					}

					if (d[cur.Y + 1, cur.X] > nd) {
						d[cur.Y + 1, cur.X] = nd;
						q.Enqueue(new Position {
							X = cur.X,
							Y = cur.Y + 1,
							D = nd,
							IsBlack = s[cur.Y + 1][cur.X] == '#'
						});
					}
				}
			}

			int ans = d[h - 1, w - 1];
			Console.WriteLine(ans);
		}

		struct Position
		{
			public int X { get; set; }
			public int Y { get; set; }
			public int D { get; set; }
			public bool IsBlack { get; set; }
		}
	}

	public static class Helper
	{
		public static void UpdateMin32<T>(T array, int index, int value) where T : IList<int>
			=> array[index] = Math.Min(array[index], value);
		public static void UpdateMax32<T>(T array, int index, int value) where T : IList<int>
			=> array[index] = Math.Max(array[index], value);
		public static void UpdateMin64<T>(T array, int index, long value) where T : IList<long>
			=> array[index] = Math.Min(array[index], value);
		public static void UpdateMax64<T>(T array, int index, long value) where T : IList<long>
			=> array[index] = Math.Max(array[index], value);

		public static T[] Array<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToArray();
		public static List<T> List<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToList();
	}

	public class Scanner2
	{
		private readonly char[] delimiter_ = new char[] { ' ' };
		private readonly string filePath_;
		private readonly Func<string> reader_;
		private string[] buf_;
		private int index_;

		public Scanner2(string file = "")
		{
			if (string.IsNullOrWhiteSpace(file)) {
				reader_ = Console.ReadLine;
			} else {
				filePath_ = file;
				var fs = new StreamReader(file);
				reader_ = fs.ReadLine;
			}
			buf_ = new string[0];
			index_ = 0;
		}

		public string Next()
		{
			if (index_ < buf_.Length) {
				return buf_[index_++];
			}

			string st = reader_();
			while (st == "") {
				st = reader_();
			}

			buf_ = st.Split(delimiter_, StringSplitOptions.RemoveEmptyEntries);
			if (buf_.Length == 0) {
				return Next();
			}

			index_ = 0;
			return buf_[index_++];
		}

		public int Int() => int.Parse(Next());
		public long Long() => long.Parse(Next());
		public double Double() => double.Parse(Next());

		public int[] ArrayInt(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Int() + add;
			}
			return Array;
		}

		public long[] ArrayLong(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Long() + add;
			}
			return Array;
		}

		public double[] ArrayDouble(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Double() + add;
			}
			return Array;
		}

		public void Save(string text)
		{
			if (string.IsNullOrWhiteSpace(filePath_)) {
				return;
			}

			File.WriteAllText(filePath_ + "_output.txt", text);
		}
	}
}

Measured memory_bytes: 11360