#include <bits/stdc++.h>
using namespace std;
vector<pair<int, int> > s[500005];
int bad[500005], inb[500005];
vector<int> a, b;
void dfs(int u)
{
while (s[u].size())
{
int v=s[u].back().first, w=s[u].back().second;
s[u].pop_back();
if (bad[w])
continue;
bad[w]=1;
dfs(v);
}
a.push_back(u);
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, m;
cin >> n >> m;
for (int i=1; i<=m; i++)
{
int u, v;
cin >> u >> v;
s[u].push_back({v, i});
s[v].push_back({u, i});
}
dfs(1);
for (int u:a)
{
if (inb[u])
{
while (b.back()!=u)
{
cout << b.back() << ' ';
inb[b.back()]=0;
b.pop_back();
}
cout << u << '\n';
}
else
{
inb[u]=1;
b.push_back(u);
}
}
}
