#include <iostream>
#include <unordered_set>
#include <algorithm>
#include <cassert>
#include <bitset>
#include <vector>
using namespace std;
const int MAXN = 5e5 + 123;
vector<int> edg[MAXN];
vector<int> find_euler_cycle() {
vector<int> ans;
vector<int> stck = {0};
while (stck.size()) {
int v = stck.back();
if (edg[v].empty()) {
ans.push_back(v);
stck.pop_back();
} else {
int u = edg[v].back();
edg[v].pop_back();
auto it = lower_bound(edg[u].begin(), edg[u].end(), v);
if (it < edg[u].end() && *it == v) {
stck.push_back(u);
}
}
}
return ans;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int n, m;
cin >> n >> m;
for (int i = 0; i < m; ++i) {
int u, v;
cin >> u >> v;
--u, --v;
edg[u].push_back(v);
edg[v].push_back(u);
}
for (int i = 0; i < n; ++i)
sort(edg[i].begin(), edg[i].end());
vector<int> ans = find_euler_cycle();
//for (auto x : ans)
//cout << x + 1 << ' ';
//cout << endl;
vector<int> stck;
bitset<MAXN> used;
for (auto x : ans) {
vector<int> ccl;
while (used[x]) {
used[stck.back()] = 0;
ccl.push_back(stck.back());
stck.pop_back();
}
if (ccl.size()) {
for (auto x : ccl)
cout << x + 1 << ' ';
cout << '\n';
}
stck.push_back(x);
used[x] = 1;
}
}
