#include <bits/stdc++.h>
using namespace std;
const int N=5e5+1;
int n,m;
vector<int>sol[N];
vector<pair<int,int>>adj[N];
void citeste()
{
cin>>n>>m;
for(int i=1; i<=m; i++)
{
int a,b;
cin>>a>>b;
adj[a].push_back({b,i});
adj[b].push_back({a,i});
}
}
bool used[N];
int seen[N];
stack<int>path;
int cnt;
bool viz[N];
void dfs(int nod)
{
viz[nod]=true;
for(auto [x,y]:adj[nod])
{
if(used[y]==true)
continue;
used[y]=true;
dfs(x);
}
path.push(nod);
seen[nod]++;
if(seen[nod]==2)
{
cnt++;
seen[nod]=1;
sol[cnt].push_back(nod);
path.pop();
while(path.top()!=nod)
{
sol[cnt].push_back(path.top());
seen[path.top()]--;
path.pop();
}
}
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
citeste();
dfs(1);
for(int i=1; i<=cnt; i++)
{
for(auto u:sol[i])
cout<<u<<" ";
cout<<'\n';
}
return 0;
}
