#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "C:\debug.h"
#else
#define debug(...) 42
#endif
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<int> deg(n);
vector<vector<pair<int, int>>> g(n);
for (int i = 0; i < m; ++i) {
int u, v;
cin >> u >> v;
--u, --v;
++deg[u], ++deg[v];
g[u].push_back({v, i});
g[v].push_back({u, i});
}
for (int i = 0; i < n; ++i) {
assert(deg[i] % 2 == 0);
}
vector<int> res;
vector<bool> used(m);
auto dfs = [&](auto self, int u) -> void {
while (g[u].size()) {
auto [v, id] = g[u].back();
g[u].pop_back();
if (used[id]) {
continue;
}
used[id] = 1;
self(self, v);
}
res.push_back(u);
};
dfs(dfs, 0);
assert((int) res.size() == m + 1);
vector<bool> in(n);
vector<int> st;
vector<vector<int>> cyc;
for (int i = 0; i <= m; ++i) {
if (in[res[i]]) {
cyc.push_back({res[i]});
while (st.size() && st.back() != res[i]) {
cyc.back().push_back(st.back());
in[st.back()] = 0;
st.pop_back();
}
} else {
in[res[i]] = 1;
st.push_back(res[i]);
}
}
assert((int) st.size() == 1 && st[0] == 0);
for (auto &v : cyc) {
for (int u : v) {
cout << u + 1 << " ";
}
cout << "\n";
}
}
