#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5e5 + 10;
int marc[MAXN], edge[MAXN];
vector<pair<int, int>> adj[MAXN];
vector<int> path;
void dfs(int v){
while(!adj[v].empty()){
auto [u, i] = adj[v].back();
adj[v].pop_back();
if(edge[i]) continue;
edge[i] = 1;
dfs(u);
}
path.push_back(v);
}
int main(){
cin.tie(0)->sync_with_stdio(0);
int n, m; cin >> n >> m;
while(m--){
int a, b; cin >> a >> b;
adj[a].push_back({b, m});
adj[b].push_back({a, m});
}
dfs(1);
stack<int> tour;
for(auto v : path){
if(marc[v]){
while(tour.top() != v){
cout << tour.top() << " ";
marc[tour.top()] --;
tour.pop();
}
cout << v << "\n";
} else{
marc[v] ++;
tour.push(v);
}
}
return 0;
}
