#[allow(unused_imports)]
#[cfg(feature = "dbg")]
use dbg::lg;
use hopkarp::hopkarp;
use std::collections::HashMap;

const MAX: usize = 500_001;

fn main() {
    let mut buf = ngtio::with_stdin();
    let h = buf.usize();
    let w = buf.usize();
    let mut a = vec![Vec::new(); MAX];
    for i in 0..h {
        for j in 0..w {
            a[buf.usize()].push([i, j]);
        }
    }
    let mut ans = 0;
    for v in a[1..].iter().rev().filter(|v| !v.is_empty()) {
        let mut is = HashMap::new();
        let mut js = HashMap::new();
        for &[i, j] in v {
            if is.get(&i).is_none() {
                let x = is.len();
                is.insert(i, x);
            };
            if js.get(&j).is_none() {
                let x = js.len();
                js.insert(j, x);
            };
        }
        let mut g = vec![Vec::new(); is.len()];
        v.iter()
            .map(|&[i, j]| [is[&i], js[&j]])
            .for_each(|[i, j]| g[i].push(j));
        let aug = hopkarp(js.len(), &g).count;
        ans += aug;
    }
    println!("{}", ans);
}

// hopkarp {{{
#[allow(dead_code)]
mod hopkarp {
    use std::collections::VecDeque;

    #[derive(Clone, Debug, Default, Hash, PartialEq)]
    pub struct HopkarpResult {
        pub count: usize,
        pub forward: Box<[Option<usize>]>,
        pub backward: Box<[Option<usize>]>,
        pub left: Box<[bool]>,
        pub right: Box<[bool]>,
    }

    pub fn hopkarp(w: usize, graph: &[Vec<usize>]) -> HopkarpResult {
        let h = graph.len();
        let mut forward = vec![None; h].into_boxed_slice();
        let mut backward = vec![None; w].into_boxed_slice();
        let (left, right) = loop {
            let dist = bfs(graph, &forward, &backward);
            if !dfs(&graph, &dist, &mut forward, &mut backward) {
                break construct_minimum_cut(graph, &dist, &backward);
            }
        };
        let count = forward.iter().filter(|b| b.is_some()).count();
        HopkarpResult {
            count,
            forward,
            backward,
            left,
            right,
        }
    }

    fn construct_minimum_cut(
        graph: &[Vec<usize>],
        dist: &[u32],
        backward: &[Option<usize>],
    ) -> (Box<[bool]>, Box<[bool]>) {
        use std::u32::MAX;
        let left = dist
            .iter()
            .map(|&x| x != MAX)
            .collect::<Vec<_>>()
            .into_boxed_slice();
        let mut right = vec![false; backward.len()].into_boxed_slice();
        for x in left.iter().enumerate().filter(|&(_, &b)| b).map(|(x, _)| x) {
            graph[x]
                .iter()
                .copied()
                .filter(|&y| backward[y] != Some(x))
                .for_each(|y| right[y] = true);
        }
        (left, right)
    }

    fn dfs(
        graph: &[Vec<usize>],
        dist: &[u32],
        forward: &mut [Option<usize>],
        backward: &mut [Option<usize>],
    ) -> bool {
        fn rec(
            x: usize,
            graph: &[Vec<usize>],
            dist: &[u32],
            used: &mut [bool],
            forward: &mut [Option<usize>],
            backward: &mut [Option<usize>],
        ) -> bool {
            used[x] = true;
            for &y in &graph[x] {
                let found = if let Some(z) = backward[y] {
                    !used[z]
                        && dist[x] + 1 == dist[z]
                        && rec(z, graph, dist, used, forward, backward)
                } else {
                    true
                };
                if found {
                    backward[y] = Some(x);
                    forward[x] = Some(y);
                    return true;
                }
            }
            false
        }
        let mut has_aug = false;
        let mut used = vec![false; forward.len()];
        for x in 0..used.len() {
            if forward[x].is_none() {
                has_aug |= rec(x, graph, dist, &mut used, forward, backward);
            }
        }
        has_aug
    }

    fn bfs(
        graph: &[Vec<usize>],
        forward: &[Option<usize>],
        backward: &[Option<usize>],
    ) -> Vec<u32> {
        use std::u32::MAX;
        let mut dist = vec![MAX; forward.len()];
        let mut queue = forward
            .iter()
            .enumerate()
            .filter(|&(_, b)| b.is_none())
            .map(|(i, _)| i)
            .inspect(|&i| dist[i] = 0)
            .collect::<VecDeque<_>>();
        while let Some(x) = queue.pop_front() {
            for &y in &graph[x] {
                if let Some(z) = backward[y] {
                    if dist[z] == MAX {
                        dist[z] = dist[x] + 1;
                        queue.push_back(z);
                    }
                }
            }
        }
        dist
    }
}
// }}}
// template {{{
#[cfg(not(feature = "dbg"))]
#[allow(unused_macros)]
#[macro_export]
macro_rules! lg {
    ($($expr:expr),*) => {};
}

#[allow(dead_code)]
mod ngtio {

    mod i {
        use std::{
            io::{self, BufRead},
            iter,
        };

        pub use self::{
            multi_token::{Leaf, Parser, ParserTuple, RawTuple, Tuple, VecLen},
            token::{Token, Usize1},
        };

        pub fn with_stdin() -> Tokenizer<io::BufReader<io::Stdin>> {
            io::BufReader::new(io::stdin()).tokenizer()
        }

        pub fn with_str(src: &str) -> Tokenizer<&[u8]> {
            src.as_bytes().tokenizer()
        }

        pub struct Tokenizer<S: BufRead> {
            queue: Vec<String>, // FIXME: String のみにすると速そうです。
            scanner: S,
        }
        macro_rules! prim_method {
            ($name:ident: $T:ty) => {
                pub fn $name(&mut self) -> $T {
                    <$T>::leaf().parse(self)
                }
            };
            ($name:ident) => {
                prim_method!($name: $name);
            };
        }
        macro_rules! prim_methods {
            ($name:ident: $T:ty; $($rest:tt)*) => {
                prim_method!($name:$T);
                prim_methods!($($rest)*);
            };
            ($name:ident; $($rest:tt)*) => {
                prim_method!($name);
                prim_methods!($($rest)*);
            };
            () => ()
        }
        impl<S: BufRead> Tokenizer<S> {
            pub fn token(&mut self) -> String {
                self.load();
                self.queue.pop().expect("入力が終了したのですが。")
            }
            pub fn new(scanner: S) -> Self {
                Self {
                    queue: Vec::new(),
                    scanner,
                }
            }
            fn load(&mut self) {
                while self.queue.is_empty() {
                    let mut s = String::new();
                    let length = self.scanner.read_line(&mut s).unwrap(); // 入力が UTF-8 でないときにエラーだそうです。
                    if length == 0 {
                        break;
                    }
                    self.queue = s.split_whitespace().rev().map(str::to_owned).collect();
                }
            }

            pub fn skip_line(&mut self) {
                assert!(
                    self.queue.is_empty(),
                    "行の途中で呼ばないでいただきたいです。現在のトークンキュー: {:?}",
                    &self.queue
                );
                self.load();
            }

            pub fn end(&mut self) {
                self.load();
                assert!(self.queue.is_empty(), "入力はまだあります！");
            }

            pub fn parse<T: Token>(&mut self) -> T::Output {
                T::parse(&self.token())
            }

            pub fn parse_collect<T: Token, B>(&mut self, n: usize) -> B
            where
                B: iter::FromIterator<T::Output>,
            {
                iter::repeat_with(|| self.parse::<T>()).take(n).collect()
            }

            pub fn tuple<T: RawTuple>(&mut self) -> <T::LeafTuple as Parser>::Output {
                T::leaf_tuple().parse(self)
            }

            pub fn vec<T: Token>(&mut self, len: usize) -> Vec<T::Output> {
                T::leaf().vec(len).parse(self)
            }

            pub fn vec_tuple<T: RawTuple>(
                &mut self,
                len: usize,
            ) -> Vec<<T::LeafTuple as Parser>::Output> {
                T::leaf_tuple().vec(len).parse(self)
            }

            pub fn vec2<T: Token>(&mut self, height: usize, width: usize) -> Vec<Vec<T::Output>> {
                T::leaf().vec(width).vec(height).parse(self)
            }

            pub fn vec2_tuple<T>(
                &mut self,
                height: usize,
                width: usize,
            ) -> Vec<Vec<<T::LeafTuple as Parser>::Output>>
            where
                T: RawTuple,
            {
                T::leaf_tuple().vec(width).vec(height).parse(self)
            }
            prim_methods! {
                u8; u16; u32; u64; u128; usize;
                i8; i16; i32; i64; i128; isize;
                f32; f64;
                char; string: String;
            }
        }

        mod token {
            use super::multi_token::Leaf;
            use std::{any, fmt, marker, str};

            pub trait Token: Sized {
                type Output;
                fn parse(s: &str) -> Self::Output;
                fn leaf() -> Leaf<Self> {
                    Leaf(marker::PhantomData)
                }
            }

            impl<T> Token for T
            where
                T: str::FromStr,
                <T as str::FromStr>::Err: fmt::Debug,
            {
                type Output = T;
                fn parse(s: &str) -> Self::Output {
                    s.parse().unwrap_or_else(|_| {
                        panic!("Parse error!: ({}: {})", s, any::type_name::<T>(),)
                    })
                }
            }

            pub struct Usize1 {}
            impl Token for Usize1 {
                type Output = usize;
                fn parse(s: &str) -> Self::Output {
                    usize::parse(s)
                        .checked_sub(1)
                        .expect("Parse error! (Zero substruction error of Usize1)")
                }
            }
        }

        mod multi_token {
            use super::{Token, Tokenizer};
            use std::{io::BufRead, iter, marker};

            pub trait Parser: Sized {
                type Output;
                fn parse<S: BufRead>(&self, server: &mut Tokenizer<S>) -> Self::Output;
                fn vec(self, len: usize) -> VecLen<Self> {
                    VecLen { len, elem: self }
                }
            }
            pub struct Leaf<T>(pub(super) marker::PhantomData<T>);
            impl<T: Token> Parser for Leaf<T> {
                type Output = T::Output;
                fn parse<S: BufRead>(&self, server: &mut Tokenizer<S>) -> T::Output {
                    server.parse::<T>()
                }
            }

            pub struct VecLen<T> {
                pub len: usize,
                pub elem: T,
            }
            impl<T: Parser> Parser for VecLen<T> {
                type Output = Vec<T::Output>;
                fn parse<S: BufRead>(&self, server: &mut Tokenizer<S>) -> Self::Output {
                    iter::repeat_with(|| self.elem.parse(server))
                        .take(self.len)
                        .collect()
                }
            }

            pub trait RawTuple {
                type LeafTuple: Parser;
                fn leaf_tuple() -> Self::LeafTuple;
            }
            pub trait ParserTuple {
                type Tuple: Parser;
                fn tuple(self) -> Self::Tuple;
            }
            pub struct Tuple<T>(pub T);
            macro_rules! impl_tuple {
                ($($t:ident: $T:ident),*) => {
                    impl<$($T),*> Parser for Tuple<($($T,)*)>
                        where
                            $($T: Parser,)*
                            {
                                type Output = ($($T::Output,)*);
#[allow(unused_variables)]
                                fn parse<S: BufRead >(&self, server: &mut Tokenizer<S>) -> Self::Output {
                                    match self {
                                        Tuple(($($t,)*)) => {
                                            ($($t.parse(server),)*)
                                        }
                                    }
                                }
                            }
                    impl<$($T: Token),*> RawTuple for ($($T,)*) {
                        type LeafTuple = Tuple<($(Leaf<$T>,)*)>;
                        fn leaf_tuple() -> Self::LeafTuple {
                            Tuple(($($T::leaf(),)*))
                        }
                    }
                    impl<$($T: Parser),*> ParserTuple for ($($T,)*) {
                        type Tuple = Tuple<($($T,)*)>;
                        fn tuple(self) -> Self::Tuple {
                            Tuple(self)
                        }
                    }
                };
            }
            impl_tuple!();
            impl_tuple!(t1: T1);
            impl_tuple!(t1: T1, t2: T2);
            impl_tuple!(t1: T1, t2: T2, t3: T3);
            impl_tuple!(t1: T1, t2: T2, t3: T3, t4: T4);
            impl_tuple!(t1: T1, t2: T2, t3: T3, t4: T4, t5: T5);
            impl_tuple!(t1: T1, t2: T2, t3: T3, t4: T4, t5: T5, t6: T6);
            impl_tuple!(t1: T1, t2: T2, t3: T3, t4: T4, t5: T5, t6: T6, t7: T7);
            impl_tuple!(
                t1: T1,
                t2: T2,
                t3: T3,
                t4: T4,
                t5: T5,
                t6: T6,
                t7: T7,
                t8: T8
            );
        }

        trait Scanner: BufRead + Sized {
            fn tokenizer(self) -> Tokenizer<Self> {
                Tokenizer::new(self)
            }
        }
        impl<R: BufRead> Scanner for R {}
    }

    pub use self::i::{with_stdin, with_str};

    pub mod prelude {
        pub use super::i::{Parser, ParserTuple, RawTuple, Token, Usize1};
    }
}
// }}}