#include<bits/stdc++.h>
using namespace std;
const int N = 5e5 + 5;
int n, m, x[N], y[N], a[3 * N], sz;
vector < int > g[N];
bool used[N];
vector < int > q;
void dfs(int v){
while(!g[v].empty()){
int num = g[v].back();
g[v].pop_back();
if(used[num]){
continue;
}
used[num] = true;
int to = (x[num] ^ v ^ y[num]);
dfs(to);
}
a[++sz] = v;
}
inline void read(int &x){
x = 0;
char c = getchar_unlocked();
while(c < '0' || c > '9'){
c = getchar_unlocked();
}
while('0' <= c && c <= '9'){
x = x * 10 + c - '0';
c = getchar_unlocked();
}
}
inline void print(int x){
int len = 0;
while(x % 10 == 0){
len += 1;
x /= 10;
}
int y = 0;
while(x){
y = y * 10 + x % 10;
x /= 10;
}
while(y){
putchar_unlocked('0' + y % 10);
y /= 10;
}
while(len--){
putchar_unlocked('0');
}
}
int main(){
read(n);
read(m);
for(int i = 1; i <= m; i++){
read(x[i]);
read(y[i]);
g[x[i]].push_back(i);
g[y[i]].push_back(i);
}
dfs(1);
memset(used, 0, sizeof(used));
vector < int > s;
for(int i = 1; i <= sz; i++){
int it = a[i];
if(!used[it]){
used[it] = true;
s.push_back(it);
}
else{
while(s.back() != it){
print(s.back());
putchar_unlocked(' ');
used[s.back()] = false;
s.pop_back();
}
print(it);
putchar_unlocked('\n');
}
}
}
