// -*- coding:utf-8-unix -*-
// #![feature(map_first_last)]
#![allow(dead_code)]
#![allow(unused_imports)]
#![allow(unused_macros)]
use std::collections::*;
use std::convert::*;
use std::convert::{From, Into};
use std::fmt::Debug;
use std::fs::File;
use std::io::prelude::*;
use std::io::*;
use std::marker::Copy;
use std::mem::*;
use std::ops::Bound::*;
use std::ops::{Add, Mul, Neg, Sub};
use std::str;
use std::thread::park_timeout;
use std::vec;
use std::{cmp, process::Output};
use std::{cmp::Ordering, env::consts::DLL_PREFIX};
use std::{cmp::Ordering::*, f32::consts::PI};

const INF: i64 = 1223372036854775807;
const UINF: usize = INF as usize;
const FINF: f64 = 122337203685.0;
const INF128: i128 = 1223372036854775807000000000000;
const LINF: i64 = 2147483647;
const MOD: i64 = 1000000007;
// const MOD: i64 = 998244353;
// const MOD: i64 = INF;

const UMOD: usize = MOD as usize;
use std::cmp::*;
use std::collections::*;
use std::io::stdin;
use std::io::stdout;
use std::io::Write;

macro_rules! p {
    ($x:expr) => {
        println!("{}", $x);
    };
}
macro_rules! d {
    ($x:expr) => {
        println!("{:?}", $x);
    };
}
macro_rules! dd {
    (x:expr) => {
        dbg!(x);
    };
}

// use str::Chars;

// use str::Chars;
#[allow(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn readi() -> (i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    iter.next().unwrap().parse::<i64>().unwrap()
}

#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}
#[allow(dead_code)]
fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[allow(dead_code)]
fn readii() -> (i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}

fn readff() -> (f64, f64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<f64>().unwrap(),
        iter.next().unwrap().parse::<f64>().unwrap(),
    )
}

#[allow(dead_code)]
fn readiii() -> (i64, i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}
#[allow(dead_code)]
fn readuu() -> (usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

fn readcc() -> (char, char) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<char>().unwrap(),
        iter.next().unwrap().parse::<char>().unwrap(),
    )
}

#[allow(dead_code)]
fn readuuu() -> (usize, usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

#[allow(dead_code)]
fn readuuuu() -> (usize, usize, usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

fn readiiii() -> (i64, i64, i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}

fn topo_sort_dfs(
    v: usize,
    graph: &Vec<Vec<(usize, usize)>>,
    used: &mut Vec<usize>,
    data: &mut Vec<usize>,
) {
    if used[v] == 1 {
        return;
    }

    used[v] = 1;
    for i in graph[v].iter() {
        let nv = (*i).0;
        if used[nv] == 1 {
            continue;
        }
        topo_sort_dfs(nv, &graph, used, data);
    }
    data.push(v);
    return;
}
fn topo_cycle_ditect(graph: &Vec<Vec<(usize, usize)>>, sorted: &Vec<usize>) -> bool {
    let mut flg = false;
    // let mut  = 0 as usize;
    let mut n = graph.len();
    let mut num = vec![0; n];
    for i in 0..n {
        num[sorted[i]] = i;
    }
    for i in 0..n {
        let mut v = i;
        for j in 0..graph[v].len() {
            let mut nv = graph[v][j].0;
            if num[v] > num[nv] {
                flg = true;
            }
        }
    }
    return flg;
}
fn topo_sort(graph: &Vec<Vec<(usize, usize)>>) -> Vec<usize> {
    let mut n = graph.len();
    // let mut = 0 as usize;c
    let mut used = vec![0; n];
    let mut res = vec![0; 0];
    let mut flg = true;
    for i in 0..n {
        topo_sort_dfs(i, &graph, &mut used, &mut res);
    }
    res.reverse();

    let mut flg_cycle = true;
    if flg_cycle {
        if topo_cycle_ditect(&graph, &res) {
            return vec![0; 0];
        }
    }
    return res;
}

fn solve() {
    let (n, m) = readuu();
    let mut graph = vec![vec![(0 as usize, 0 as usize); (0) as usize]; (n) as usize];
    for i in 0..m {
        let (mut a, mut b) = readuu();
        a -= 1;
        b -= 1;
        graph[a].push((b, 1));
    }
    let ts = topo_sort(&graph);
    let mut visited = vec![0; n];
    let mut res = vec![];
    for i in 0..n {
        let v = ts[i];
        for j in 0..graph[v].len() {
            let nv = graph[v][j].0;
            if visited[nv] == 0 {
                visited[nv] = 1;

                res.push((v + 1, nv + 1));
            }
        }
    }
    p!(res.len());
    for i in 0..res.len() {
        println!("{} {}", res[i].0, res[i].1);
    }
    return;
}

fn main() {
    solve();
}