fn main() {
    let mut io = IO::new();
    input! { from io,
        n: usize, m: usize,
        mut edges: [(Usize1, Usize1); m]
    }

    assert!(2 <= n && n <= 100_000);
    assert!(m <= 200_000);
    for &(u, v) in &edges {
        assert!(u < n);
        assert!(v < n);
        assert_ne!(u, v);
    }
    edges.sort();
    edges.dedup();
    if edges.len() != m {
        eprintln!("多重辺あり")
    }
    let mut scc = SccGraph::new(n);
    for &(u, v) in &edges {
        scc.add_edge(u, v);
    }
    let grouping = scc.scc();
    let n_group = grouping.len();
    if n_group == 1 {
        io.println(0);
        return;
    }
    let mut ids = vec![0; n];
    for (g, l) in grouping.iter().enumerate() {
        for &v in l.iter() {
            ids[v] = g;
        }
    }
    let mut new_in = vec![0; n_group];
    let mut new_out = vec![0; n_group];
    for &(u, v) in &edges {
        if ids[u] != ids[v] {
            new_out[ids[u]] += 1;
            new_in[ids[v]] += 1;
        }
    }
    let ans = new_in
        .iter()
        .filter(|&&x| x == 0)
        .count()
        .max(new_out.iter().filter(|&&x| x == 0).count());
    io.println(ans);
}

use scc::SccGraph;

pub mod scc {
    use crate::internal_scc;
    pub struct SccGraph {
        internal: internal_scc::SccGraph,
    }

    impl SccGraph {
        pub fn new(n: usize) -> Self {
            SccGraph {
                internal: internal_scc::SccGraph::new(n),
            }
        }

        pub fn add_edge(&mut self, from: usize, to: usize) {
            let n = self.internal.num_vertices();
            assert!(from < n);
            assert!(to < n);
            self.internal.add_edge(from, to);
        }

        pub fn scc(&self) -> Vec<Vec<usize>> {
            self.internal.scc()
        }
    }
}

pub mod internal_scc {
    pub struct Csr<E> {
        start: Vec<usize>,
        elist: Vec<E>,
    }

    impl<E> Csr<E>
    where
        E: Copy,
    {
        pub fn new(n: usize, edges: &[(usize, E)], init: E) -> Self {
            let mut csr = Csr {
                start: vec![0; n + 1],
                elist: vec![init; edges.len()],
            };
            for e in edges.iter() {
                csr.start[e.0 + 1] += 1;
            }
            for i in 1..=n {
                csr.start[i] += csr.start[i - 1];
            }
            let mut counter = csr.start.clone();
            for e in edges.iter() {
                csr.elist[counter[e.0]] = e.1;
                counter[e.0] += 1;
            }
            csr
        }
    }

    #[derive(Copy, Clone)]
    struct _Edge {
        to: usize,
    }

    /// Reference:
    /// R. Tarjan,
    /// Depth-First Search and Linear Graph Algorithms
    pub struct SccGraph {
        n: usize,
        edges: Vec<(usize, _Edge)>,
    }

    impl SccGraph {
        pub fn new(n: usize) -> Self {
            SccGraph { n, edges: vec![] }
        }

        pub fn num_vertices(&self) -> usize {
            self.n
        }

        pub fn add_edge(&mut self, from: usize, to: usize) {
            self.edges.push((from, _Edge { to }));
        }

        /// return pair of (# of scc, scc id)
        pub fn scc_ids(&self) -> (usize, Vec<usize>) {
            // In C++ ac-library, this function is implemented by using recursive lambda functions.
            // Instead, we use fn and struct for capturing environments.
            struct _Env {
                g: Csr<_Edge>,
                now_ord: usize,
                group_num: usize,
                visited: Vec<usize>,
                low: Vec<usize>,
                ord: Vec<Option<usize>>,
                ids: Vec<usize>,
            }
            let mut env = _Env {
                g: Csr::new(self.n, &self.edges, _Edge { to: 0 }),
                now_ord: 0,
                group_num: 0,
                visited: Vec::with_capacity(self.n),
                low: vec![0; self.n],
                ord: vec![None; self.n],
                ids: vec![0; self.n],
            };

            fn dfs(v: usize, n: usize, env: &mut _Env) {
                env.low[v] = env.now_ord;
                env.ord[v] = Some(env.now_ord);
                env.now_ord += 1;
                env.visited.push(v);

                for i in env.g.start[v]..env.g.start[v + 1] {
                    let to = env.g.elist[i].to;
                    if let Some(x) = env.ord[to] {
                        env.low[v] = std::cmp::min(env.low[v], x);
                    } else {
                        dfs(to, n, env);
                        env.low[v] = std::cmp::min(env.low[v], env.low[to]);
                    }
                }
                if env.low[v] == env.ord[v].unwrap() {
                    loop {
                        let u = *env.visited.last().unwrap();
                        env.visited.pop();
                        env.ord[u] = Some(n);
                        env.ids[u] = env.group_num;
                        if u == v {
                            break;
                        }
                    }
                    env.group_num += 1;
                }
            }
            for i in 0..self.n {
                if env.ord[i].is_none() {
                    dfs(i, self.n, &mut env);
                }
            }
            for x in env.ids.iter_mut() {
                *x = env.group_num - 1 - *x;
            }
            (env.group_num, env.ids)
        }

        pub fn scc(&self) -> Vec<Vec<usize>> {
            let ids = self.scc_ids();
            let group_num = ids.0;
            let mut counts = vec![0usize; group_num];
            for &x in ids.1.iter() {
                counts[x] += 1;
            }
            let mut groups: Vec<Vec<usize>> = (0..ids.0).map(|_| vec![]).collect();
            for i in 0..group_num {
                groups[i].reserve(counts[i]);
            }
            for i in 0..self.n {
                groups[ids.1[i]].push(i);
            }
            groups
        }
    }
}

// ------------ io module start ------------
use std::io::{stdout, BufWriter, Read, StdoutLock, Write};

pub struct IO {
    iter: std::str::SplitAsciiWhitespace<'static>,
    buf: BufWriter<StdoutLock<'static>>,
}

impl IO {
    pub fn new() -> Self {
        let mut input = String::new();
        std::io::stdin().read_to_string(&mut input).unwrap();
        let input = Box::leak(input.into_boxed_str());
        let out = Box::new(stdout());
        IO {
            iter: input.split_ascii_whitespace(),
            buf: BufWriter::new(Box::leak(out).lock()),
        }
    }
    fn scan_str(&mut self) -> &'static str {
        self.iter.next().unwrap()
    }
    pub fn scan<T: Scan>(&mut self) -> <T as Scan>::Output {
        <T as Scan>::scan(self)
    }
    pub fn scan_vec<T: Scan>(&mut self, n: usize) -> Vec<<T as Scan>::Output> {
        (0..n).map(|_| self.scan::<T>()).collect()
    }
    pub fn print<T: Print>(&mut self, x: T) {
        <T as Print>::print(self, x);
    }
    pub fn println<T: Print>(&mut self, x: T) {
        self.print(x);
        self.print("\n");
    }
    pub fn iterln<T: Print, I: IntoIterator<Item = T>>(&mut self, iter: I, delim: &str) {
        let mut iter = iter.into_iter();
        if let Some(v) = iter.next() {
            self.print(v);
            for v in iter {
                self.print(delim);
                self.print(v);
            }
        }
        self.print("\n");
    }
    pub fn flush(&mut self) {
        self.buf.flush().unwrap();
    }
}

impl Default for IO {
    fn default() -> Self {
        Self::new()
    }
}

pub trait Scan {
    type Output;
    fn scan(io: &mut IO) -> Self::Output;
}

macro_rules! impl_scan {
    ($($t:tt),*) => {
        $(
            impl Scan for $t {
                type Output = Self;
                fn scan(s: &mut IO) -> Self::Output {
                    s.scan_str().parse().unwrap()
                }
            }
        )*
    };
}

impl_scan!(i16, i32, i64, isize, u16, u32, u64, usize, String, f32, f64);

impl Scan for char {
    type Output = char;
    fn scan(s: &mut IO) -> Self::Output {
        s.scan_str().chars().next().unwrap()
    }
}

pub enum Bytes {}
impl Scan for Bytes {
    type Output = &'static [u8];
    fn scan(s: &mut IO) -> Self::Output {
        s.scan_str().as_bytes()
    }
}

pub enum Chars {}
impl Scan for Chars {
    type Output = Vec<char>;
    fn scan(s: &mut IO) -> Self::Output {
        s.scan_str().chars().collect()
    }
}

pub enum Usize1 {}
impl Scan for Usize1 {
    type Output = usize;
    fn scan(s: &mut IO) -> Self::Output {
        s.scan::<usize>().wrapping_sub(1)
    }
}

impl<T: Scan, U: Scan> Scan for (T, U) {
    type Output = (T::Output, U::Output);
    fn scan(s: &mut IO) -> Self::Output {
        (T::scan(s), U::scan(s))
    }
}

impl<T: Scan, U: Scan, V: Scan> Scan for (T, U, V) {
    type Output = (T::Output, U::Output, V::Output);
    fn scan(s: &mut IO) -> Self::Output {
        (T::scan(s), U::scan(s), V::scan(s))
    }
}

impl<T: Scan, U: Scan, V: Scan, W: Scan> Scan for (T, U, V, W) {
    type Output = (T::Output, U::Output, V::Output, W::Output);
    fn scan(s: &mut IO) -> Self::Output {
        (T::scan(s), U::scan(s), V::scan(s), W::scan(s))
    }
}

pub trait Print {
    fn print(w: &mut IO, x: Self);
}

macro_rules! impl_print_int {
    ($($t:ty),*) => {
        $(
            impl Print for $t {
                fn print(w: &mut IO, x: Self) {
                    w.buf.write_all(x.to_string().as_bytes()).unwrap();
                }
            }
        )*
    };
}

impl_print_int!(i16, i32, i64, isize, u16, u32, u64, usize, f32, f64);

impl Print for u8 {
    fn print(w: &mut IO, x: Self) {
        w.buf.write_all(&[x]).unwrap();
    }
}

impl Print for &[u8] {
    fn print(w: &mut IO, x: Self) {
        w.buf.write_all(x).unwrap();
    }
}

impl Print for &str {
    fn print(w: &mut IO, x: Self) {
        w.print(x.as_bytes());
    }
}

impl Print for String {
    fn print(w: &mut IO, x: Self) {
        w.print(x.as_bytes());
    }
}

impl<T: Print + Copy> Print for &T {
    fn print(w: &mut IO, x: Self) {
        w.print(*x);
    }
}

impl<T: Print, U: Print> Print for (T, U) {
    fn print(w: &mut IO, (x, y): Self) {
        w.print(x);
        w.print(" ");
        w.print(y);
    }
}

impl<T: Print, U: Print, V: Print> Print for (T, U, V) {
    fn print(w: &mut IO, (x, y, z): Self) {
        w.print(x);
        w.print(" ");
        w.print(y);
        w.print(" ");
        w.print(z);
    }
}

pub mod neboccoio_macro {
    #[macro_export]
    macro_rules! input {
        (@start $io:tt @read @rest) => {};

        (@start $io:tt @read @rest, $($rest: tt)*) => {
            input!(@start $io @read @rest $($rest)*)
        };

        (@start $io:tt @read @rest mut $($rest:tt)*) => {
            input!(@start $io @read @mut [mut] @rest $($rest)*)
        };

        (@start $io:tt @read @rest $($rest:tt)*) => {
            input!(@start $io @read @mut [] @rest $($rest)*)
        };

        (@start $io:tt @read @mut [$($mut:tt)?] @rest $var:tt: [[$kind:tt; $len2: expr]; $len1:expr] $($rest:tt)*) => {
            let $($mut)* $var = (0..$len1).map(|_| $io.scan_vec::<$kind>($len2)).collect::<<$kind as Scan>::Output>();
            input!(@start $io @read @rest $($rest)*)
        };

        (@start $io:tt @read @mut [$($mut:tt)?] @rest $var:tt: [$kind:tt; $len:expr] $($rest:tt)*) => {
            let $($mut)* $var = $io.scan_vec::<$kind>($len);
            input!(@start $io @read @rest $($rest)*)
        };

        (@start $io:tt @read @mut [$($mut:tt)?] @rest $var:tt: $kind:tt $($rest:tt)*) => {
            let $($mut)* $var = $io.scan::<$kind>();
            input!(@start $io @read @rest $($rest)*)
        };

        (from $io:tt $($rest:tt)*) => {
            input!(@start $io @read @rest $($rest)*)
        };
    }
}

// ------------ io module end ------------