#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template <class type1>
#define ll long long int
#define endl "\n"
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
using ordered_multiset = tree <type1, null_type, less_equal <type1>, rb_tree_tag, tree_order_statistics_node_update>;
//ordered_multiset <ll> kek;(declaration for multiorder set)
// ordered_set o_set;(declaration)
//kek.order_of_key(i);(strictly less then i for multi order set)
//o_set.order_of_key(5) ;(strictly less then i for multi order set)
#define yes cout << "YES\n"
#define no cout << "NO\n"
#define mod 1000000007
ll POW(ll a,ll b)
{ ll ans=1;
while(b>0)
{ if(b%2)ans=(ans*a)%mod;
b/=2;
a=(a*a)%mod;
}
return ans;
}
const ll N=100009;
vector<ll>adj[N];
ll vis[N];
ll parent[N];
ll start,end1;
bool dfs(ll node,ll par)
{
vis[node]=1;
parent[node]=par;
for(auto u:adj[node])
{
if(u==par)continue;
if(vis[u])
{
start=u;
end1=node;
return true;
}
if(dfs(u,node))return true;
}
return false;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
ll n,m,i,j;
cin>>n>>m;
for(i=0;i<m;i++)
{
ll u,v;
cin>>u>>v;
adj[u].push_back(v);
adj[v].push_back(u);
}
ll ans=0;
for(i=1;i<=n;i++)
{
if(vis[i]==0)
{
if(dfs(i,-1))
{
ans=1;
break;
}
}
}
if(ans)
{
vector<ll>v;
v.push_back(start);
v.push_back(end1);
while(parent[end1]!=start)
{
end1=parent[end1];
v.push_back(end1);
}
v.push_back(start);
cout<<v.size()<<endl;
for(auto u:v)cout<<u<<" ";
cout<<endl;
}
else
{
cout<<"IMPOSSIBLE\n";
}
return 0;
}
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