#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
const int maxn = 5e5 + 20;
vector<int> adj[maxn] , path;
int from[maxn] , to[maxn];
bool visited[maxn];
void dfs(int v)
{
while(!adj[v].empty())
{
int e = adj[v].back() , u = from[e] ^ to[e] ^ v;
adj[v].pop_back();
if(visited[e])
continue;
visited[e] = 1;
dfs(u);
}
path.pb(v);
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n , m;
cin >> n >> m;
for(int i = 0; i < m; i++)
{
int a , b;
cin >> a >> b;
a-- , b--;
adj[a].pb(i);
adj[b].pb(i);
from[i] = a , to[i] = b;
}
dfs(0);
vector<int> tmp;
memset(visited , 0 , sizeof visited);
for(auto v : path)
{
if(visited[v])
{
while(tmp.back() != v)
cout << tmp.back() + 1 << " " , visited[tmp.back()] = 0 , tmp.pop_back();
tmp.pop_back();
cout << v + 1 << endl;
}
tmp.pb(v);
visited[v] = 1;
}
}
