#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
#define pb push_back
#define F first
#define S second
#define int long long
const int maxn = 3e3 + 10;
const int maxm = 2e5 + 1;
const int LOG = 21;
const int mod = 1e9 + 7;
int n, m;
vector<pii> G[maxn];
vector<int> path, tour;
bool mark[maxn];
int vis[maxn];
void Tour(int v) {
while (!G[v].empty()) {
auto [u, id] = G[v].back();
G[v].pop_back();
if (mark[id]) continue;
mark[id] = 1;
Tour(u);
}
path.pb(v);
}
signed main() {
cin >> n >> m;
for (int i = 1; i <= m; i++) {
int v, u;
cin >> v >> u;
G[v].pb({u, i});
G[u].pb({v, i});
}
Tour(1);
for (int v : path) {
if (vis[v]) {
while (tour.back() != v) {
cout << tour.back() << ' ';
vis[tour.back()]--;
tour.pop_back();
}
cout << v << '\n';
}
else {
tour.pb(v);
vis[v]++;
}
}
}
