#![allow(unused_imports)]
#![allow(non_snake_case, unused)]

// ---------- begin input macro ----------
// https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------


use std::cmp::*;
use std::collections::*;
use std::ops::*;
use std::marker::*;
 
const INF: i64 = std::i64::MAX/100;
const MOD: i64 = 1_000_000_007;
// const MOD: i64 = 998_244_353;

pub struct UnionFind {
    data: Vec<i32>,
}

impl UnionFind {
    pub fn new(n: usize) -> Self{
        UnionFind {
            data: vec![-1;n]
        }
    }
    pub fn root(&mut self, x: usize) -> usize{
        if self.data[x]<0 {
            x
        }
        else {
            let p = self.data[x] as usize;
            self.data[x] = self.root(p) as i32;
            self.data[x] as usize
        }
    }
    pub fn unite(&mut self, x: usize, y: usize){
        let rx = self.root(x);
        let ry = self.root(y);
        if rx!=ry {
            let (rx,ry) = if self.data[rx]<=self.data[ry] {
                (rx,ry)
            }
            else{
                (ry,rx)
            };
            self.data[rx] += self.data[ry];
            self.data[ry] = rx as i32;
        }
    }
    pub fn same(&mut self, x: usize, y: usize) ->  bool{
        self.root(x) == self.root(y)
    }
    pub fn size(&mut self, x: usize) -> i32 {
        let r = self.root(x);
        - self.data[r]
    }
}

fn main() {
    input! {
        n: usize,
        m: usize,
        uv: [(usize,usize);m],
    }
    let mut uf = UnionFind::new(n);
    let mut e = vec![vec![];n];
    for &(u,v) in &uv {
        uf.unite(u-1,v-1);
        e[u-1].push(v-1);
    }
    let mut count = 0;
    let mut map = HashMap::new();
    for i in 0..n {
        if uf.root(i)==i {
            map.insert(i,count);
            count += 1;
        }
    }
    let mut edge = vec![vec![];count];
    let mut set = vec![HashSet::new();count];
    for &(u,v) in &uv {
        let idx = *map.get(&(uf.root(u-1))).unwrap();
        edge[idx].push((u-1,v-1));
        set[idx].insert(u-1);
        set[idx].insert(v-1);
    }
    let mut ans = vec![];
    let mut inner = vec![0;n];
    for i in 0..count {
        let mut ret = vec![];
        if edge[i].len()==0 {
            continue;
        }
        for &(u,v) in &edge[i] {
            inner[v] += 1;
        }
        let mut q = VecDeque::new();
        let mut l = vec![];
        for &s in set[i].iter() {
            l.push(s);
            if inner[s]==0 {
                q.push_back(s);
            }
        }
        while let Some(v) = q.pop_front() {
            ret.push(v);
            for &e in &e[v] {
                inner[e] -= 1;
                if inner[e]==0 {
                    q.push_back(e);
                }
            }
        }
        if ret.len()==set[i].len() {
            for j in 0..ret.len()-1 {
                ans.push((ret[j],ret[j+1]));
            }
        }
        else {
            for j in 0..l.len() {
                ans.push((l[j],l[(j+1)%l.len()]));
            }
        }
    }
    println!("{}",ans.len());
    for &(s,t) in &ans {
        println!("{} {}",s+1,t+1);
    }
}