#include<bits/stdc++.h>
using namespace std;
#define MAXN (int) 5e5
#define ll long long
#define pb push_back
#define eb emplace_back
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpli vector<pli>
#define vpil vector<pil>
#define vpll vector<pll>
#define pii pair<int, int>
#define vpii vector<pii>
#define vi vector<int>
#define vvi vector<vi>
unordered_set<int> adj[MAXN];
int main(){
int n, m;
cin >> n >> m;
for (int i = 0; i < m; i++){
int u, v;
cin >> u >> v;
u--,v--;
adj[u].insert(v);
adj[v].insert(u);
}
stack<int> st;
st.push(0);
vvi paths;
vi path;
vi vis;
while (st.size()){
int u = st.top();
if (vis.size() && u == vis.front())
{
reverse(vis.begin(), vis.end());
paths.pb(vis);
vis.clear();
}
vis.pb(u);
if (adj[u].size()){
auto v = adj[u].begin();
st.push(*v);
adj[*v].erase(u);
adj[u].erase(*v);
}
else {
st.pop();
path.pb(u);
}
}
// cout << "ans: " << endl;
for (auto p : paths){
for (int i : p) cout << i + 1 << " ";
cout << endl;
}
return 0;
}
