#include <bits/stdc++.h>
// #pragma GCC optimize ("Ofast,unroll-loops")
using namespace std;
typedef long long ll;
typedef pair<int, int> pp;
#define rep(i,l,r) for(int i = (l); i < (r); i++)
#define per(i,r,l) for(int i = (r); i >= (l); i--)
#define sz(x) (int)x.size()
#define ff first
#define ss second
#define all(x) begin(x), end(x)
#define pb push_back
const ll mod = 1e9+7, maxn = 5e5+5, inf = ll(1e9)+5;
vector<pp> adj[maxn];
bool vis[maxn], mrk[maxn];
vector<pp> edge;
void dfs(int r){
vector<pp> stk{{r, -1}};
while(sz(stk)){
auto[r, lst] = stk.back();
if(lst + 1) edge.pb({r, lst}), stk.back().ss = -1;
mrk[r] = true;
if(sz(adj[r])){
auto[id, u] = adj[r].back(); adj[r].pop_back();
if(vis[id]) continue;
vis[id] = true;
stk.back().ss = u;
stk.pb({u, -1});
}else stk.pop_back();
}
}
// void dfs(int r){
// mrk[r] = true;
// while(sz(adj[r])){
// auto[id, u] = adj[r].back(); adj[r].pop_back();
// if(vis[id]) continue;
// vis[id] = true;
// dfs(u);
// edge.pb({r, u});
// }
// }
int main(){
cin.tie(0) -> sync_with_stdio(0);
#ifndef ONLINE_JUDGE
freopen("in.in", "r", stdin);
freopen("out.out", "w", stdout);
#endif
int n, m; cin >> n >> m;
rep(i,0,m){
int u, v; cin >> u >> v; u--, v--;
adj[u].pb({i, v}), adj[v].pb({i, u});
}
rep(i,0,n) if(!mrk[i]) dfs(i);
reverse(all(edge));
// for(auto[u, v]: edge) cout << ++u << ' ' << ++v << '\n';
vector<int> stk{edge[0].ff};
fill(mrk, mrk + n, false); mrk[edge[0].ff] = true;
rep(i,0,m){
auto[u, v] = edge[i];
if(mrk[v]){
while(true){
int r = stk.back(); stk.pop_back();
mrk[r] = false;
cout << r+1 << ' ';
if(r == v) break;
} cout << '\n';
}
mrk[v] = true;
stk.pb(v);
}
return 0;
}
