#include <bits/stdc++.h>
#include <cstdint>
using namespace std;
#define ll long long
#define pb push_back
#define ins insert
//cout<<fixed<<setprecision(3); 3 decimalke brez fixed pa 3 zanesljiva mesta
const int MAXN=1e6+3;
const long long linf=1e18;
const int inf=1e9;
const int mod=1e9+7;
vector<int>res;
vector<vector<pair<int,int>>>adj;
vector<int>vis;
vector<int>in;
void dfs(int e){
while(adj[e].size()){
auto ne=adj[e].back();
adj[e].pop_back();
if(vis[ne.second]) continue;
vis[ne.second]++;
dfs(ne.first);
}
if(in[e]){
cout<<e+1<<' ';
in[e]--;
while(res.back()!=e+1){
cout<<res.back()<<' ';
in[res.back()-1]--;
res.pop_back();
}
res.pop_back();
cout<<endl;
}
res.pb(e+1);
in[e]++;
}
void solve(){
int n,m;cin>>n>>m;
adj=vector<vector<pair<int,int>>>(n);
vector<int>deg(n,0);
vis=vector<int>(m,0);
in=vector<int>(n,0);
for(int i=0;i<m;i++){
int a,b;cin>>a>>b;
--a;--b;
adj[a].pb({b,i});
adj[b].pb({a,i});
deg[a]++;
deg[b]++;
}
bool ok=true;
for(int i=0;i<n;i++){
if(deg[i]&1) ok=false;
}
dfs(0);
if(!ok){
cout<< "IMPOSSIBLE"<<endl;
}
else{
}
}
int main(){
std::ios::sync_with_stdio(false);
std::cin.tie(NULL);
int t=1;
while(t--) solve();
}
