// Make the best become better
// No room for laziness
#include<bits/stdc++.h>
#define int long long
#define pb push_back
#define fi first
#define se second
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxN = 1e6 + 5;
const int mod = 1e9 + 7;
const ll oo = 1e18;
int n, m;
int id = 0;
vector<int> path;
vector<int> adj[maxN];
struct TEdge
{
int u, v;
bool del;
} e[maxN];
void ReadInput()
{
cin >> n >> m;
for(int i=1; i<=m; i++)
{
int u, v;
cin >> u >> v;
e[i] = {u, v, 0};
adj[u].pb(i);
adj[v].pb(i);
}
}
void FindEulerTour()
{
vector<int> vc;
vc.pb(1);
while(!vc.empty())
{
int u = vc.back();
while(!adj[u].empty() && e[adj[u].back()].del) adj[u].pop_back();
if(!adj[u].empty())
{
int id = adj[u].back();
adj[u].pop_back();
e[id].del = 1;
vc.pb(e[id].u ^ e[id].v ^ u);
}
else
{
path.pb(u);
vc.pop_back();
}
}
}
void Solve()
{
FindEulerTour();
int tmp = 0;
for(int u : path)
{
cout << u << " ";
if(u == tmp)
{
tmp = 0;
cout << '\n';
}
else if(!tmp) tmp = u;
}
}
int32_t main()
{
//freopen("x.inp", "r", stdin);
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
ReadInput();
Solve();
}
