#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define _ <<' '<<
#define print(x) cout<<#x<<": "<<(x)<<endl
#define vrint(v) for (const auto &e:(v)) cout<<e+1<<' '; cout<<'\n';
vector<vector<array<int, 2>>> adj;
vector<int> et, x, vis;
stack<int> s;
void dfs(const int u) {
while (!adj[u].empty()) {
const auto [v, i]=adj[u].back();
adj[u].pop_back();
if (vis[i]) continue;
vis[i]=1;
dfs(v);
et.push_back(u);
}
}
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n,m;
cin>>n>>m;
adj.resize(n);
for (int i=0; i<m; i++) {
int a,b;
cin>>a>>b;
adj[--a].push_back({--b, i});
adj[b].push_back({a, i});
}
et.reserve(m+5);
vis.assign(m, 0);
dfs(0);
reverse(et.begin(), et.end());
et.push_back(0);
x.resize(n, 0);
//vrint(et);
for (const auto e:et) {
if (x[e]) {
int v;
do {
v=s.top();
s.pop();
x[v]=0;
cout<<v+1<<' '<<flush;
} while (v!=e);
s.push(e);
x[e]=1;
cout<<'\n';
} else {
s.push(e);
x[e]=1;
}
}
}
