#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long
#define ull unsigned long long
// 217
// 44
using namespace std;
const int MAXN = (int) 5e5;
vector < pair <int, int> > g[MAXN + 1];
bool vis[MAXN + 1];
vector <int> ord;
void dfs(int nod) {
while(g[nod].size()) {
auto it = g[nod].back();
g[nod].pop_back();
if(vis[it.second] == 0) {
vis[it.second] = 1;
dfs(it.first);
}
}
ord.push_back(nod);
}
int main() {
//ifstream cin("A.in");
//ofstream cout("A.out");
int i, n, m;
ios::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
cin >> n >> m;
for(i = 1; i <= m; i++) {
int x, y;
cin >> x >> y;
g[x].push_back({y, i});
g[y].push_back({x, i});
}
dfs(1);
for(i = 1; i <= n; i++) {
vis[i] = 0;
}
int sz = ord.size();
vector <int> stk;
for(i = 0; i < sz; i++) {
if(vis[ord[i]] == 0) {
vis[ord[i]] = 1;
stk.push_back(ord[i]);
}
else {
while(stk.back() != ord[i]) {
cout << stk.back() << " ";
vis[stk.back()] = 0;
stk.pop_back();
}
cout << ord[i] << "\n";
}
}
//cout << ans;
//cin.close();
//cout.close();
return 0;
}
