#include <bits/stdc++.h>
using namespace std;
const int N = 500010;
int n, m;
vector < pair<int,int> > G[N];
vector <int> E;
bool del[N];
int pos[N];
void dfs(int u) {
while(!G[u].empty()) {
int id = G[u].back().first, v = G[u].back().second;
if (del[id]) { G[u].pop_back(); continue; }
else del[id] = 1, dfs(v);
}
E.push_back(u);
}
int main() {
//freopen("out.txt", "w", stdout);
ios_base::sync_with_stdio(false); cin.tie(0);
cin >> n >> m;
for (int i = 1; i <= m; ++i) {
int u, v; cin >> u >> v;
G[u].push_back(make_pair(i,v));
G[v].push_back(make_pair(i,u));
}
dfs(1);
//for (int u: E) cerr << u << ' '; cerr << endl;
stack <int> s;
for (int i = 0; i < (int)E.size(); ++i) {
int u = E[i];
if (!pos[u]) {
pos[u] = 1;
s.push(u);
} else {
while(s.top() != u) {
printf("%d ", s.top());
pos[s.top()] = 0;
s.pop();
}
printf("%d\n", u);
}
}
}
