use std::collections::*;
use std::io::Write;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;

fn main() {
    input! {
        h: usize,
        w: usize,
        s: [bytes; h],
    }
    let mut g = maxflow::Graph::new(h * w + 2);
    let mut edge = vec![];
    let src = h * w;
    let dst = src + 1;
    for (i, c) in s.iter().enumerate() {
        for (j, c) in c.iter().enumerate() {
            if *c == b'#' {
                continue;
            }
            if (i + j) % 2 == 0 {
                g.add_edge(src, i * w + j, 1u32);
                for &(dx, dy) in [(1, 0), (0, 1), (!0, 0), (0, !0)].iter() {
                    let (x, y) = (i + dx, j + dy);
                    if x < h && y < w && s[x][y] == b'.' {
                        edge.push(g.add_edge(i * w + j, x * w + y, 1));
                    }
                }
            } else {
                g.add_edge(i * w + j, dst, 1);
            }
        }
    }
    g.flow(src, dst);
    let mut matched = vec![None; h * w];
    let mut free = vec![vec![]; h * w];
    for e in edge.iter() {
        let (s, t, u, _) = g.get_edge(e);
        if u == 1 {
            matched[s] = Some(t);
            matched[t] = Some(s);
        } else {
            free[s].push(t);
            free[t].push(s);
        }
    }
    let mut win = vec![false; h * w];
    for i in 0..(h * w) {
        if win[i] {
            continue;
        }
        if s[i / w][i % w] == b'#' {
            continue;
        }
        if matched[i].is_some() {
            continue;
        }
        win[i] = true;
        let mut dfs = vec![i];
        while let Some(v) = dfs.pop() {
            for &u in free[v].iter() {
                let t = matched[u].unwrap();
                if !win[t] {
                    win[t] = true;
                    dfs.push(t);
                }
            }
        }
    }
    println!("{}", win.iter().filter(|w| **w).count());
}

// ---------- 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 max flow (Dinic) ----------
mod maxflow {
    pub trait MaxFlowCapacity:
        Copy + Ord + std::ops::Add<Output = Self> + std::ops::Sub<Output = Self>
    {
        fn zero() -> Self;
        fn inf() -> Self;
    }

    macro_rules! impl_primitive_integer_capacity {
        ($x:ty, $y:expr) => {
            impl MaxFlowCapacity for $x {
                fn zero() -> Self {
                    0
                }
                fn inf() -> Self {
                    $y
                }
            }
        };
    }

    impl_primitive_integer_capacity!(u32, std::u32::MAX);
    impl_primitive_integer_capacity!(u64, std::u64::MAX);
    impl_primitive_integer_capacity!(i32, std::i32::MAX);
    impl_primitive_integer_capacity!(i64, std::i64::MAX);

    #[derive(Clone)]
    struct Edge<Cap> {
        to_: u32,
        inv_: u32,
        cap_: Cap,
    }

    impl<Cap> Edge<Cap> {
        fn new(to: usize, inv: usize, cap: Cap) -> Self {
            Edge {
                to_: to as u32,
                inv_: inv as u32,
                cap_: cap,
            }
        }
        fn to(&self) -> usize {
            self.to_ as usize
        }
        fn inv(&self) -> usize {
            self.inv_ as usize
        }
    }

    impl<Cap: MaxFlowCapacity> Edge<Cap> {
        fn add(&mut self, cap: Cap) {
            self.cap_ = self.cap_ + cap;
        }
        fn sub(&mut self, cap: Cap) {
            self.cap_ = self.cap_ - cap;
        }
        fn cap(&self) -> Cap {
            self.cap_
        }
    }

    pub struct Graph<Cap> {
        graph: Vec<Vec<Edge<Cap>>>,
    }

    #[allow(dead_code)]
    pub struct EdgeIndex {
        src: usize,
        dst: usize,
        x: usize,
        y: usize,
    }

    impl<Cap: MaxFlowCapacity> Graph<Cap> {
        pub fn new(size: usize) -> Self {
            Self {
                graph: vec![vec![]; size],
            }
        }
        pub fn add_edge(&mut self, src: usize, dst: usize, cap: Cap) -> EdgeIndex {
            assert!(src.max(dst) < self.graph.len());
            assert!(cap >= Cap::zero());
            assert!(src != dst);
            let x = self.graph[src].len();
            let y = self.graph[dst].len();
            self.graph[src].push(Edge::new(dst, y, cap));
            self.graph[dst].push(Edge::new(src, x, Cap::zero()));
            EdgeIndex { src, dst, x, y }
        }
        // src, dst, used, intial_capacity
        #[allow(dead_code)]
        pub fn get_edge(&self, e: &EdgeIndex) -> (usize, usize, Cap, Cap) {
            let max = self.graph[e.src][e.x].cap() + self.graph[e.dst][e.y].cap();
            let used = self.graph[e.dst][e.y].cap();
            (e.src, e.dst, used, max)
        }
        pub fn flow(&mut self, src: usize, dst: usize) -> Cap {
            let size = self.graph.len();
            assert!(src.max(dst) < size);
            assert!(src != dst);
            let mut queue = std::collections::VecDeque::new();
            let mut level = vec![0; size];
            let mut it = vec![0; size];
            let mut ans = Cap::zero();
            loop {
                (|| {
                    level.clear();
                    level.resize(size, 0);
                    level[src] = 1;
                    queue.clear();
                    queue.push_back(src);
                    while let Some(v) = queue.pop_front() {
                        let d = level[v] + 1;
                        for e in self.graph[v].iter() {
                            let u = e.to();
                            if e.cap() > Cap::zero() && level[u] == 0 {
                                level[u] = d;
                                if u == dst {
                                    return;
                                }
                                queue.push_back(u);
                            }
                        }
                    }
                })();
                if level[dst] == 0 {
                    break;
                }
                it.clear();
                it.resize(size, 0);
                loop {
                    let f = self.dfs(dst, src, Cap::inf(), &mut it, &level);
                    if f == Cap::zero() {
                        break;
                    }
                    ans = ans + f;
                }
            }
            ans
        }
        fn dfs(&mut self, v: usize, src: usize, cap: Cap, it: &mut [usize], level: &[u32]) -> Cap {
            if v == src {
                return cap;
            }
            while let Some((u, inv)) = self.graph[v].get(it[v]).map(|p| (p.to(), p.inv())) {
                if level[u] + 1 == level[v] && self.graph[u][inv].cap() > Cap::zero() {
                    let cap = cap.min(self.graph[u][inv].cap());
                    let c = self.dfs(u, src, cap, it, level);
                    if c > Cap::zero() {
                        self.graph[v][it[v]].add(c);
                        self.graph[u][inv].sub(c);
                        return c;
                    }
                }
                it[v] += 1;
            }
            Cap::zero()
        }
    }
}
// ---------- end max flow (Dinic) ----------