use std::collections::*;

type Deque<T> = VecDeque<T>;

fn main() {
    input! {
        h: usize,
        w: usize,
        s: [bytes; h],
    }
    let mut diff = vec![0usize];
    for i in 1..=3 {
        diff.push(i);
        diff.push(!i + 1);
    }
    let mut s = s;
    for s in s.iter_mut() {
        s.insert(0, b'#');
        s.push(b'#');
    }
    s.insert(0, vec![b'#'; w + 2]);
    s.push(vec![b'#'; w + 2]);
    let inf = std::u32::MAX / 10;
    let mut dp = vec![vec![inf; w + 2]; h + 2];
    let mut deq = Deque::new();
    for i in 4..=h {
        dp[i][0] = 0;
        deq.push_back((i, 0));
    }
    for j in 1..=(w - 4) {
        dp[h + 1][j] = 0;
        deq.push_back((h + 1, j));
    }
    while let Some((x, y)) = deq.pop_front() {
        let d = dp[x][y];
        for dx in diff.iter() {
            for dy in diff.iter() {
                let x = x + *dx;
                let y = y + *dy;
                if !(x < h + 2 && y < w + 2) {
                    continue;
                }
                if (x < 4 && y < 4) || (x >= h - 2 && y >= w - 2) {
                    continue;
                }
                if s[x][y] == b'#' {
                    if dp[x][y].chmin(d) {
                        deq.push_front((x, y));
                    }
                } else {
                    if dp[x][y].chmin(d + 1) {
                        deq.push_back((x, y));
                    }
                }
            }
        }
    }
    let mut ans = inf;
    for i in 1..=(h - 3) {
        ans.chmin(dp[i][w + 1]);
    }
    for j in 4..=w {
        ans.chmin(dp[0][j]);
    }
    println!("{}", ans);
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------
// ---------- begin chmin, chmax ----------
pub trait ChangeMinMax {
    fn chmin(&mut self, x: Self) -> bool;
    fn chmax(&mut self, x: Self) -> bool;
}

impl<T: PartialOrd> ChangeMinMax for T {
    fn chmin(&mut self, x: Self) -> bool {
        *self > x && {
            *self = x;
            true
        }
    }
    fn chmax(&mut self, x: Self) -> bool {
        *self < x && {
            *self = x;
            true
        }
    }
}
// ---------- end chmin, chmax ----------