#![allow(unused_imports, unused_macros)]

use kyoproio::*;
use std::{
    collections::*,
    io::{self, prelude::*},
    iter,
    mem::{replace, swap},
};

fn main() -> io::Result<()> {
    std::thread::Builder::new()
        .stack_size(64 * 1024 * 1024)
        .spawn(solve)?
        .join()
        .unwrap();
    Ok(())
}

fn solve() {
    let stdin = io::stdin();
    let mut kin = KInput::new(stdin.lock());
    let stdout = io::stdout();
    let mut out = io::BufWriter::new(stdout.lock());
    macro_rules! output { ($($args:expr),+) => { write!(&mut out, $($args),+).unwrap(); }; }
    macro_rules! outputln {
        ($($args:expr),+) => { output!($($args),+); outputln!(); };
        () => { output!("\n"); if cfg!(debug_assertions) { out.flush().unwrap(); } }
    }

    let (h, w): (usize, usize) = kin.input();
    let s: Vec<Vec<u8>> = kin.seq(h);
    let mut dinic = Dinic::new(h * w + 2);
    let mut add = |i1, j1, i2, j2| {
        let mut u = w * i1 + j1;
        let mut v = w * i2 + j2;
        if (i1 + j1) & 1 == 1 {
            swap(&mut u, &mut v);
        }
        dinic.add_edge(u, v, 1);
    };
    let mut cnt = [0; 2];
    for i in 0..h {
        for j in 0..w {
            if s[i][j] != b'.' {
                let p = i + j & 1;
                cnt[p] += 1;
                if i + 1 < h && s[i + 1][j] != b'.' {
                    add(i, j, i + 1, j);
                }
                if j + 1 < w && s[i][j + 1] != b'.' {
                    add(i, j, i, j + 1);
                }
            }
        }
    }
    for i in 0..h {
        for j in 0..w {
            let p = i + j & 1;
            if s[i][j] != b'.' {
                if p == 0 {
                    dinic.add_edge(h * w, w * i + j, 1);
                } else {
                    dinic.add_edge(w * i + j, h * w + 1, 1);
                }
            }
        }
    }
    let m = dinic.run(h * w, h * w + 1).0;
    let ans = 100 * m + 10 * (cnt[0] - m).min(cnt[1] - m) + (cnt[0] - cnt[1]).abs();
    outputln!("{}", ans);
}

pub struct Dinic {
    g: Vec<Vec<(usize, bool)>>,
    es: Vec<(usize, usize, i64)>,
}
impl Dinic {
    pub fn new(n: usize) -> Self {
        Self {
            g: vec![Vec::new(); n],
            es: Vec::new(),
        }
    }
    pub fn add_edge(&mut self, u: usize, v: usize, cap: i64) {
        self.g[u].push((self.es.len(), true));
        self.g[v].push((self.es.len(), false));
        self.es.push((u, v, cap));
    }
    fn edge(&self, flow: &[i64], i: usize, fw: bool) -> (usize, i64) {
        let (u, v, c) = self.es[i];
        if fw {
            (v, c - flow[i])
        } else {
            (u, flow[i])
        }
    }
    pub fn run(&self, s: usize, t: usize) -> (i64, Vec<i64>) {
        let mut flow = vec![0; self.es.len()];
        let mut sum = 0;
        loop {
            let mut dist = vec![!0; self.g.len()];
            dist[s] = 0;
            let mut que = VecDeque::new();
            que.push_back(s);
            'bfs: while let Some(u) = que.pop_front() {
                for (v, r) in self.g[u].iter().map(|&(i, fw)| self.edge(&flow, i, fw)) {
                    if dist[v] == !0 && r > 0 {
                        dist[v] = dist[u] + 1;
                        if v == t {
                            break 'bfs;
                        }
                        que.push_back(v);
                    }
                }
            }
            let add = self.dfs(&mut flow, &mut dist, s, t, i64::max_value());
            if add == 0 {
                break;
            }
            sum += add;
        }
        (sum, flow)
    }
    fn dfs(&self, flow: &mut [i64], dist: &mut [usize], u: usize, t: usize, cap: i64) -> i64 {
        if u == t {
            return cap;
        }
        let mut add = 0;
        for &(i, fw) in &self.g[u] {
            let (v, r) = self.edge(&flow, i, fw);
            if dist[v] == dist[u] + 1 && r > 0 {
                let a = self.dfs(flow, dist, v, t, (cap - add).min(r));
                if a > 0 {
                    if fw {
                        flow[i] += a;
                    } else {
                        flow[i] -= a;
                    }
                    add += a;
                } else {
                    dist[v] = 0;
                }
            }
        }
        add
    }
}

// -----------------------------------------------------------------------------
pub mod kyoproio {
    use std::io::prelude::*;
    pub trait Input {
        fn str(&mut self) -> &str;
        fn input<T: InputParse>(&mut self) -> T {
            T::input(self)
        }
        fn iter<T: InputParse>(&mut self) -> Iter<T, Self> {
            Iter(self, std::marker::PhantomData)
        }
        fn seq<T: InputParse, B: std::iter::FromIterator<T>>(&mut self, n: usize) -> B {
            self.iter().take(n).collect()
        }
    }
    pub struct KInput<R> {
        src: R,
        buf: String,
        pos: usize,
    }
    impl<R: BufRead> KInput<R> {
        pub fn new(src: R) -> Self {
            Self {
                src,
                buf: String::with_capacity(1024),
                pos: 0,
            }
        }
    }
    impl<R: BufRead> Input for KInput<R> {
        fn str(&mut self) -> &str {
            loop {
                if self.pos >= self.buf.len() {
                    self.pos = 0;
                    self.buf.clear();
                    if self.src.read_line(&mut self.buf).expect("io error") == 0 {
                        return &self.buf;
                    }
                }
                let range = self.pos
                    ..self.buf[self.pos..]
                        .find(|c: char| c.is_ascii_whitespace())
                        .map(|i| i + self.pos)
                        .unwrap_or_else(|| self.buf.len());
                self.pos = range.end + 1;
                if range.end > range.start {
                    return &self.buf[range];
                }
            }
        }
    }
    pub struct Iter<'a, T, I: ?Sized>(&'a mut I, std::marker::PhantomData<*const T>);
    impl<'a, T: InputParse, I: Input + ?Sized> Iterator for Iter<'a, T, I> {
        type Item = T;
        fn next(&mut self) -> Option<T> {
            Some(self.0.input())
        }
    }
    pub trait InputParse: Sized {
        fn input<I: Input + ?Sized>(src: &mut I) -> Self;
    }
    impl InputParse for Vec<u8> {
        fn input<I: Input + ?Sized>(src: &mut I) -> Self {
            src.str().as_bytes().to_owned()
        }
    }
    macro_rules! from_str_impl {
        { $($T:ty)* } => {
            $(impl InputParse for $T {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    src.str().parse::<$T>().expect("parse error")
                }
            })*
        }
    }
    from_str_impl! {
        String char bool f32 f64 isize i8 i16 i32 i64 i128 usize u8 u16 u32 u64 u128
    }
    macro_rules! tuple_impl {
        ($H:ident $($T:ident)*) => {
            impl<$H: InputParse, $($T: InputParse),*> InputParse for ($H, $($T),*) {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    ($H::input(src), $($T::input(src)),*)
                }
            }
            tuple_impl!($($T)*);
        };
        () => {}
    }
    tuple_impl!(A B C D E F G);
}