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#include<iostream>
#include<iomanip>
#include<vector>
#include<algorithm>
#include<tuple>
#include<functional>
#include<numeric>
#include<random>
#include<unordered_map>
#include<set>
#include<map>
#include<unordered_set>
#include<cassert>
#include<cmath>
#include<queue>
#include<stack>
#include<sstream>
// #define endl '\n'
using namespace std;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
using sstream=stringstream;
template<typename T1,typename T2=T1> using P=pair<T1,T2>;
template<typename T> using V=vector<T>;
template<typename T> using F=function<T>;
void _debug() {cerr << '\n';}
template <typename A, typename... B>
void _debug(A a, B... b) {cerr << a << ' ', _debug(b...);}
#define debug(...) cerr << '(' << (#__VA_ARGS__) << ") : ", _debug(__VA_ARGS__)
template<typename T>
ostream& operator<<(ostream& os,const V<T>& v){
    for(const auto& i:v)
        os<<i<<' ';
    return os;
}
template<typename T>
ostream& operator<<(ostream& os,const unordered_set<T>& v){
    for(const auto& i:v)
        os<<i<<' ';
    return os;
}
template<typename T1,typename T2>
ostream& operator<<(ostream& os,const P<T1,T2>& p){
    return os<<'('<<p.first<<','<<p.second<<") ";
}
mt19937 mt(hash<string>()(":poop:"));
constexpr int inf=0x3f3f3f3f;
constexpr ll infll=0x3f3f3f3f3f3f3f3f;
constexpr int mod=1e9+7;
inline void init(){

}
inline void solve() {
    int n,m;cin>>n>>m;
    V<V<P<ll,int>>> e(n);
    V<bool> vis(m,false);
    V<int> out(n,0);
    for(int i=0;i<m;i++){
        int a,b;cin>>a>>b;a--,b--;
        e[a].emplace_back(b,i);
        e[b].emplace_back(a,i);
        out[a]++,out[b]++;
    }
    if(!out[0]){
        cout<<"IMPOSSIBLE"<<endl;
        return;
    }
    for(auto i:out)
        if(i&1){
            cout<<"IMPOSSIBLE"<<endl;
            return;
        }
    // debug(out);
    V<int> ans{1};
    F<void(int,int,int)> dfs=[&](int u,int v,int i){
        if(vis[i]) return;
        vis[i]=true;
        for(auto [x,j]:e[v])
            if(!vis[j]) dfs(v,x,j);
        ans.emplace_back(u+1);
    };
    for(auto [v,i]:e[0])
        dfs(0,v,i);
    if((int)ans.size()!=m+1){
        cout<<"IMPOSSIBLE"<<endl;
        return;
    }
    for(auto i:ans)
        cout<<i<<' ';
}
signed main(){
    // cin.tie(nullptr)->sync_with_stdio(false);
    signed T=1;
    // cin>>T;
    init();
    while(T--)
        solve();
    return 0;
}