import java.io.*;
import java.math.*;
import java.util.*;
public class Main {  //Any contiguous line of wall blocks can be deleted
	//in one move since there always exists an invertible rectangle to do so
 
	public static void main(String[] args) { 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int R = I.nextInt();
		int C = I.nextInt();
		char[][] grid = new char[R][C];
		int[][] dp = new int[R][C];
		for (int i = 0; i < R; i++) grid[i] = I.next().toCharArray();
		if (grid[0][0]=='#') dp[0][0]=1;
		for (int r = 1; r < R; r++) {
			dp[r][0]=dp[r-1][0]; //Only way is from above
			if (grid[r][0]=='#'&&grid[r-1][0]=='.') dp[r][0]++; //New contiguous line of
			//wall needs one more operation
		}
		for (int c = 1; c < C; c++) {
			dp[0][c]=dp[0][c-1]; //Only way to square is from the left
			if (grid[0][c]=='#'&&grid[0][c-1]=='.') dp[0][c]++;
		}
		for (int r = 1; r < R; r++) {
			for (int c = 1; c < C; c++) {
				int up = dp[r-1][c];
				int left = dp[r][c-1];
				if (grid[r][c]=='#'&&grid[r-1][c]=='.') up++;
				if (grid[r][c]=='#'&&grid[r][c-1]=='.') left++;
				dp[r][c]=Math.min(left, up);
			}
		}
		O.pln(dp[R-1][C-1]);
	}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
		double nextDouble() {return Double.parseDouble(next());}
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	}
}



Measured memory_bytes: 25904