#![allow(unused_imports, unused_macros, dead_code)]

macro_rules! min {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        it.next().map(|z| it.fold(z, |x, y| min!(x, y)))
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = min!($($ys),*);
        if $x < t { $x } else { t }
    }}
}
macro_rules! max {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        it.next().map(|z| it.fold(z, |x, y| max!(x, y)))
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = max!($($ys),*);
        if $x > t { $x } else { t }
    }}
}
macro_rules! ewriteln {
    ($($args:expr),*) => { let _ = writeln!(&mut std::io::stderr(), $($args),*); };
}
macro_rules! trace {
    ($x:expr) => { ewriteln!(">>> {} = {:?}", stringify!($x), $x) };
    ($($xs:expr),*) => { trace!(($($xs),*)) }
}
macro_rules! put {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        if let Some(x) = it.next() { print!("{}", x); }
        for x in it { print!(" {}", x); }
        println!("");
    }};
    ($x:expr) => { println!("{}", $x) };
    ($x:expr, $($xs:expr),*) => { print!("{} ", $x); put!($($xs),*) }
}

const M: i64 = 1_000_000_007;

fn main() {
    let mut sc = Scanner::new();
    let h: usize = sc.cin();
    let w: usize = sc.cin();
    let f: Vec<Vec<char>> = (0..h).map(|_| sc.chars()).collect();

    let mut memo: Vec<Vec<usize>> = vec![vec![0; w]; h];
    for i in 0..h {
        for j in 0..w {
            memo[i][j] = if i == 0 && j == 0 {
                if f[0][0] == '#' {
                    1
                } else {
                    0
                }
            } else if i == 0 {
                if f[i][j] == '.' {
                    memo[i][j - 1]
                } else {
                    memo[i][j - 1] + if f[i][j - 1] == '.' { 1 } else { 0 }
                }
            } else if j == 0 {
                if f[i][j] == '.' {
                    memo[i - 1][j]
                } else {
                    memo[i - 1][j] + if f[i - 1][j] == '.' { 1 } else { 0 }
                }
            } else {
                if f[i][j] == '.' {
                    min!(memo[i - 1][j], memo[i][j - 1])
                } else {
                    min!(
                        memo[i][j - 1] + if f[i][j - 1] == '.' { 1 } else { 0 },
                        memo[i - 1][j] + if f[i - 1][j] == '.' { 1 } else { 0 })
                }
            }
            ;
        }
        // trace!(&memo[i]);
    }
    put!(memo[h-1][w-1]);

}

use std::io::{self, Write};
use std::str::FromStr;
use std::collections::VecDeque;

struct Scanner { stdin: io::Stdin, buffer: VecDeque<String>, }
impl Scanner {
    fn new() -> Self { Scanner { stdin: io::stdin(), buffer: VecDeque::new() } }
    fn cin<T: FromStr>(&mut self) -> T {
        while self.buffer.len() == 0 {
            let mut line = String::new();
            let _ = self.stdin.read_line(&mut line);
            for w in line.split_whitespace() {
                self.buffer.push_back(String::from(w));
            }
        }
        self.buffer.pop_front().unwrap().parse::<T>().ok().unwrap()
    }
    fn chars(&mut self) -> Vec<char> { self.cin::<String>().chars().collect() }
    fn vec<T: FromStr>(&mut self, n: usize) -> Vec<T> { (0..n).map(|_| self.cin()).collect() }
}


Measured memory_bytes: 4352