#[doc = " https://github.com/hatoo/competitive-rust-snippets"]
#[allow(unused_imports)]
use std::cmp::{max, min, Ordering};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Write};
#[allow(unused_imports)]
use std::iter::FromIterator;
#[allow(unused_macros)]
macro_rules ! debug { ( $ ( $ a : expr ) ,* ) => { eprintln ! ( concat ! ( $ ( stringify ! ( $ a ) , " = {:?}, " ) ,* ) , $ ( $ a ) ,* ) ; } }
#[macro_export]
macro_rules ! input { ( source = $ s : expr , $ ( $ r : tt ) * ) => { let mut parser = Parser :: from_str ( $ s ) ; input_inner ! { parser , $ ( $ r ) * } } ; ( parser = $ parser : ident , $ ( $ r : tt ) * ) => { input_inner ! { $ parser , $ ( $ r ) * } } ; ( new_stdin_parser = $ parser : ident , $ ( $ r : tt ) * ) => { let stdin = std :: io :: stdin ( ) ; let reader = std :: io :: BufReader :: new ( stdin . lock ( ) ) ; let mut $ parser = Parser :: new ( reader ) ; input_inner ! { $ parser , $ ( $ r ) * } } ; ( $ ( $ r : tt ) * ) => { input ! { new_stdin_parser = parser , $ ( $ r ) * } } ; }
#[macro_export]
macro_rules ! input_inner { ( $ parser : ident ) => { } ; ( $ parser : ident , ) => { } ; ( $ parser : ident , $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let $ var = read_value ! ( $ parser , $ t ) ; input_inner ! { $ parser $ ( $ r ) * } } ; }
#[macro_export]
macro_rules ! read_value { ( $ parser : ident , ( $ ( $ t : tt ) ,* ) ) => { ( $ ( read_value ! ( $ parser , $ t ) ) ,* ) } ; ( $ parser : ident , [ $ t : tt ; $ len : expr ] ) => { ( 0 ..$ len ) . map ( | _ | read_value ! ( $ parser , $ t ) ) . collect ::< Vec < _ >> ( ) } ; ( $ parser : ident , chars ) => { read_value ! ( $ parser , String ) . chars ( ) . collect ::< Vec < char >> ( ) } ; ( $ parser : ident , usize1 ) => { read_value ! ( $ parser , usize ) - 1 } ; ( $ parser : ident , $ t : ty ) => { $ parser . next ::<$ t > ( ) . expect ( "Parse error" ) } ; }
use std::io;
use std::io::BufRead;
use std::str;
pub struct Parser<R> {
    reader: R,
    buf: Vec<u8>,
    pos: usize,
}
impl Parser<io::Empty> {
    pub fn from_str(s: &str) -> Parser<io::Empty> {
        Parser {
            reader: io::empty(),
            buf: s.as_bytes().to_vec(),
            pos: 0,
        }
    }
}
impl<R: BufRead> Parser<R> {
    pub fn new(reader: R) -> Parser<R> {
        Parser {
            reader: reader,
            buf: vec![],
            pos: 0,
        }
    }
    pub fn update_buf(&mut self) {
        self.buf.clear();
        self.pos = 0;
        loop {
            let (len, complete) = {
                let buf2 = self.reader.fill_buf().unwrap();
                self.buf.extend_from_slice(buf2);
                let len = buf2.len();
                if len == 0 {
                    break;
                }
                (len, buf2[len - 1] <= 0x20)
            };
            self.reader.consume(len);
            if complete {
                break;
            }
        }
    }
    pub fn next<T: str::FromStr>(&mut self) -> Result<T, T::Err> {
        loop {
            let mut begin = self.pos;
            while begin < self.buf.len() && (self.buf[begin] <= 0x20) {
                begin += 1;
            }
            let mut end = begin;
            while end < self.buf.len() && (self.buf[end] > 0x20) {
                end += 1;
            }
            if begin != self.buf.len() {
                self.pos = end;
                return str::from_utf8(&self.buf[begin..end]).unwrap().parse::<T>();
            } else {
                self.update_buf();
            }
        }
    }
}
#[allow(unused_macros)]
macro_rules ! debug { ( $ ( $ a : expr ) ,* ) => { eprintln ! ( concat ! ( $ ( stringify ! ( $ a ) , " = {:?}, " ) ,* ) , $ ( $ a ) ,* ) ; } }
#[doc = " https://github.com/hatoo/competitive-rust-snippets"]
const BIG_STACK_SIZE: bool = true;
#[allow(dead_code)]
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}
fn minmax(p: (usize, usize)) -> (usize, usize) {
    if p.0 <= p.1 {
        p
    } else {
        (p.1, p.0)
    }
}

struct LowLink<'a> {
    g: &'a [Vec<usize>],
    used: Vec<bool>,
    ord: Vec<usize>,
    low: Vec<usize>,
    articulation: Vec<usize>,
    bridge: Vec<(usize, usize)>,
}

impl <'a> LowLink<'a> {
    fn new(g: &'a [Vec<usize>]) -> LowLink {
        let n = g.len();
        let mut used = vec![false; n];
        let mut ord = vec![0; n];
        let mut low = vec![0; n];
        let articulation = vec![];
        let bridge = vec![];
        LowLink {
            g,
            used,
            ord,
            low,
            articulation,
            bridge,
        }
    }
    fn build(&mut self) {
        self.do_build(0, 0, None);
        self.articulation.sort();
        self.bridge.sort();
    }
    fn do_build(&mut self, u: usize, k: usize, par: Option<usize>) -> usize {
        let mut k = k;
        self.used[u] = true;
        self.ord[u] = k;
        k += 1;
        self.low[u] = self.ord[u];
        let mut is_articulation = false;
        let mut cnt = 0;
        for &v in &self.g[u] {
            if !self.used[v] {
               cnt += 1; 
               k = self.do_build(v, k, Some(u));
               self.low[u] = std::cmp::min(self.low[u], self.low[v]);
               is_articulation |= par.is_some() && self.low[v] >= self.ord[u];
               if self.ord[u] < self.low[v] {
                   self.bridge.push(minmax((u, v)));
               }
            } else if Some(v) != par {
                self.low[u] = std::cmp::min(self.low[u], self.ord[v]);
            } else {}
        }
        is_articulation |= par.is_none() && cnt > 1;
        if is_articulation {
            self.articulation.push(u);
        }
        k
    }
}
fn solve() {
    input! {
        V: usize, E: usize,
        ES: [(usize, usize); E],
    }

    let mut g = vec![vec![]; V];
    for i in 0..E {
        let (s,t) = ES[i];
        g[s].push(t);
        g[t].push(s);
    }

    let mut lowlink = LowLink::new(&g);
    lowlink.build();

    let mut bri = lowlink.bridge;
    bri.sort();

    for x in bri {
        println!("{} {}", x.0, x.1);
    }
}


Measured memory_bytes: 11136