#include <bits/stdc++.h>
using namespace std;
const int maxn=5e5+10;
int di[4]={1,-1,0,0};
int dj[4]={0,0,-1,1};
int n,m;
bool vis[maxn];
int ma[maxn];
vector<pair<int,int>>g[maxn];
vector<int>path;
void dfs(int node)
{
while(!g[node].empty())
{
auto ax=g[node].back();
g[node].pop_back();
if(vis[ax.second])continue;
vis[ax.second]=1;
dfs(ax.first);
}
path.push_back(node);
ma[node]++;
if(ma[node]==2)
{
cout<<node+1<< " ";
path.pop_back();
while(path.back()!=node)
{
cout<<path.back()+1<<" ";
ma[path.back()]--;
path.pop_back();
}
cout<<endl;
ma[node]=1;
}
}
int main()
{
ios_base::sync_with_stdio(false); cin.tie(0);
cin>>n>>m;
memset(vis,0,sizeof vis);
for(int i=0;i<m;i++)
{
int x,y;
cin>>x>>y;
x--;y--;
g[x].push_back({y,i});
g[y].push_back({x,i});
}
memset(ma,0,sizeof ma);
dfs(0);
return 0;
}
