macro_rules ! input { ( source = $ s : expr , $ ( $ r : tt ) * ) => { let mut iter = $ s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; ( iter = $ iter : ident , $ ( $ r : tt ) * ) => { let s = { use std :: io :: Read ; let mut s = String :: new ( ) ; std :: io :: stdin ( ) . read_to_string ( & mut s ) . unwrap ( ) ; s } ; let mut $ iter = s . split_whitespace ( ) ; input_inner ! { $ iter , $ ( $ r ) * } } ; ( $ ( $ r : tt ) * ) => { let s = { use std :: io :: Read ; let mut s = String :: new ( ) ; std :: io :: stdin ( ) . read_to_string ( & mut s ) . unwrap ( ) ; s } ; let mut iter = s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; }
macro_rules ! input_inner { ( $ iter : expr ) => { } ; ( $ iter : expr , ) => { } ; ( $ iter : expr , mut $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let mut $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , mut $ var : ident $ ( $ r : tt ) * ) => { input_inner ! { $ iter , mut $ var : usize $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident $ ( $ r : tt ) * ) => { input_inner ! { $ iter , $ var : usize $ ( $ r ) * } } ; }
macro_rules ! read_value { ( $ iter : expr , ( $ ( $ t : tt ) ,* ) ) => { ( $ ( read_value ! ( $ iter , $ t ) ) ,* ) } ; ( $ iter : expr , [ $ t : tt ; $ len : expr ] ) => { ( 0 ..$ len ) . map ( | _ | read_value ! ( $ iter , $ t ) ) . collect ::< Vec < _ >> ( ) } ; ( $ iter : expr , { chars : $ base : expr } ) => { read_value ! ( $ iter , String ) . chars ( ) . map ( | c | ( c as u8 - $ base as u8 ) as usize ) . collect ::< Vec < usize >> ( ) } ; ( $ iter : expr , { char : $ base : expr } ) => { read_value ! ( $ iter , { chars : $ base } ) [ 0 ] } ; ( $ iter : expr , chars ) => { read_value ! ( $ iter , String ) . chars ( ) . collect ::< Vec < char >> ( ) } ; ( $ iter : expr , char ) => { read_value ! ( $ iter , chars ) [ 0 ] } ; ( $ iter : expr , usize1 ) => { read_value ! ( $ iter , usize ) - 1 } ; ( $ iter : expr , $ t : ty ) => { $ iter . next ( ) . unwrap ( ) . parse ::<$ t > ( ) . unwrap ( ) } ; }
#[derive(Clone, Copy, Debug, Default)]
pub struct Adjacent {
    pub to: usize,
    pub id: usize,
}
impl Adjacent {
    pub fn new(to: usize, id: usize) -> Adjacent {
        Adjacent { to: to, id: id }
    }
}
#[derive(Clone, Debug, Default)]
pub struct Graph {
    pub vsize: usize,
    pub esize: usize,
    pub graph: Vec<Vec<Adjacent>>,
}
impl Graph {
    pub fn new(vsize: usize) -> Graph {
        Graph {
            vsize: vsize,
            esize: 0,
            graph: vec![vec![]; vsize],
        }
    }
    pub fn add_edge(&mut self, from: usize, to: usize) {
        self.graph[from].push(Adjacent::new(to, self.esize));
        self.esize += 1;
    }
    pub fn add_undirected_edge(&mut self, u: usize, v: usize) {
        self.graph[u].push(Adjacent::new(v, self.esize));
        self.graph[v].push(Adjacent::new(u, self.esize));
        self.esize += 1;
    }
    pub fn vertexes(&self) -> std::ops::Range<usize> {
        0..self.vsize
    }
    pub fn adjacency(&self, from: usize) -> &Vec<Adjacent> {
        &self.graph[from]
    }
}
#[derive(Debug)]
pub struct GraphRec {
    n: usize,
    m: usize,
    visited: Vec<bool>,
    out: Vec<usize>,
    ab: Vec<(usize, usize)>,
}
impl GraphRec {
    pub fn new(n: usize, ab: Vec<(usize, usize)>) -> GraphRec {
        let m = ab.len();
        GraphRec {
            n: n,
            m: m,
            visited: vec![false; n],
            out: vec![0; n],
            ab: ab,
        }
    }
    pub fn dfs(&mut self, u: usize, p: Option<usize>, graph: &Graph) {
        for v in graph.adjacency(u) {
            if !self.visited[v.to] {
                self.out[self.ab[v.id].0] -= 1;
                self.visited[v.to] = true;
                self.dfs(v.to, Some(v.id), graph);
            }
        }
        if let Some(i) = p {
            let v = if self.ab[i].0 == u {
                self.ab[i].1
            } else {
                self.ab[i].0
            };
            self.ab[i] = if self.out[u] % 2 == 1 { (u, v) } else { (v, u) };
            self.out[self.ab[i].0] += 1;
        }
    }
}
fn main() {
    input! { n, m, ab: [(usize1, usize1); m] };
    if m % 2 == 1 {
        println!("{}", -1);
        return;
    }
    let mut graph = Graph::new(n);
    let mut rec = GraphRec::new(n, ab);
    for &(a, b) in rec.ab.iter() {
        graph.add_undirected_edge(a, b);
        rec.out[a] += 1;
    }
    rec.visited[0] = true;
    rec.dfs(0, None, &graph);
    for i in 0..m {
        println!("{} {}", rec.ab[i].0 + 1, rec.ab[i].1 + 1);
    }
}


Measured memory_bytes: 29308