#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define REP(i,n) for(long long i = 0; i < (n); i++)
#define FOR(i, m, n) for(long long i = (m);i < (n); ++i)
#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);

template<class T> using V = vector<T>;
template<class T, class U> using P = pair<T, U>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQR = priority_queue<T,vector<T>,greater<T>>;

constexpr long long MOD = (long long)1e9 + 7;
constexpr long long MOD2 = 998244353;
constexpr long long HIGHINF = (long long)1e18;
constexpr long long LOWINF = (long long)1e15;
constexpr long double PI = 3.1415926535897932384626433;

template <class T> vector<T> make_v(size_t N,T init){return vector<T>(N,init);}
template <class... T> auto make_v(size_t N,T... t){return vector<decltype(make_v(t...))>(N,make_v(t...));}
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template <class T, class U>ostream &operator<<(ostream &o, const map<T, U>&obj) {o << "{"; for (auto &x : obj) o << " {" << x.first << " : " << x.second << "}" << ","; o << " }"; return o;}
template <class T>ostream &operator<<(ostream &o, const set<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const multiset<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const vector<T>&obj) {o << "{"; for (int i = 0; i < (int)obj.size(); ++i)o << (i > 0 ? ", " : "") << obj[i]; o << "}"; return o;}
template <class T, class U>ostream &operator<<(ostream &o, const pair<T, U>&obj) {o << "{" << obj.first << ", " << obj.second << "}"; return o;}
template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
void print(void) {cout << endl;}
template <class Head> void print(Head&& head) {cout << head;print();}
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) {cout << head << " ";print(forward<Tail>(tail)...);}
template <class T> void chmax(T& a, const T b){a=max(a,b);}
template <class T> void chmin(T& a, const T b){a=min(a,b);}
void YN(bool flg) {cout << (flg ? "YES" : "NO") << endl;}
void Yn(bool flg) {cout << (flg ? "Yes" : "No") << endl;}
void yn(bool flg) {cout << (flg ? "yes" : "no") << endl;}

vector<vector<pair<int,int>>> edge;
vector<int> depth,parent;

void dfs(int from) {
	for(auto e:edge[from]){
		int to = e.first;
		if(depth[to]==-1){
			depth[to]=depth[from]+1;
			parent[to] = e.second;
			dfs(to);
		}
	}
}

int main() {
	int N,M; cin >> N >> M;
	vector<int> A(M),B(M);
	edge.resize(N);
	depth.resize(N,-1);
	parent.resize(N,-1);
	for(int i = 0; i < M; ++i) {
		int A,B;
		cin >> A >> B;
		A--,B--;
		edge[A].push_back({B,i});
		edge[B].push_back({A,i});
	}
	depth[0] = 0;
	dfs(0);
	vector<int> idx(N);
	iota(ALL(idx),0);
	sort(ALL(idx),[&](int l, int r){return depth[l]>depth[r];});
	vector<int> flg(M,1);
	vector<pair<int,int>> ans;
	for(int n = 0; n < N; ++n) {
		int i = idx[n];
		int cnt = 0;
		for(auto e:edge[i]) cnt += flg[e.second];

		if(cnt%2){
			corner(i==0,-1);
			for(auto e:edge[i]) if(flg[e.second] && e.second != parent[i]) {
				ans.push_back({i,e.first});
				flg[e.second] = 0;
			}
		}
		else{
			for(auto e:edge[i]) if(flg[e.second]) {
				ans.push_back({i,e.first});
				flg[e.second] = 0;
			}
		}
	}
	for(auto e:ans) cout << e.first+1 << " " << e.second+1 << endl;

	return 0;
}


Measured memory_bytes: 13300