#include <fstream>
#include <list>
#include <queue>
#include <stack>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueueler.out");

#define TR( C, it ) \
    for( list<int>::iterator it = C.begin(); it != C.end(); it++ )
#define pb push_back

#define NX 100010

list<int> G[NX], P;
stack<int> S;
queue<int> Q;

int N, M, deg[NX], viz[NX];

void readGraph()
{
    int u,v;
    fin>>N>>M;
    while(M--)
    {
        fin>>u>>v;
        G[u].pb(v); deg[u]++; // Add the adiacent vertex to
        G[v].pb(u); deg[v]++; // the list of edges and increment degree
    }
}
// Check if graph is still connected when we remove a edge
// Marks the viz[i] = 1 for all vertexes conex with 1
void BFS(int v)
{
    Q.push(v); viz[v]=1;
    while(!Q.empty())
    {
        v = Q.front(); Q.pop();
        TR( G[v], u ) // bullshit parser error
            if(!viz[*u])
                Q.push(*u), viz[*u]=1;
    }
}

bool isConnected()
{
    BFS(1);
    for(int v=2; v<=N; ++v)
        if(viz[v]==0)
            return true; // According to the BFS, it wasn't visited
    return false;
}

bool isEulerian()
{
    if(!isConnected()) // A eulerian graph must be connected
        return false;
    
    for(int v=1; v<=N; v++) // The degrees must be even
        if(deg[v]%2!=0)
            return false;
    
    return true;
}

void eraseEdge(int v, int u)
{
    deg[v]--; deg[u]--;
    G[v].pop_front(); // erase first edge (aleator)
    TR( G[u], it )
        if( *it == v)
        {
            G[u].erase(it);
            break;
        }
}

void euler(int v)
{
    while(!G[v].empty())
    {
        int u = G[v].front();
        S.push(v);
        eraseEdge(v, u);
        v=u;
    }
}

bool fetchResult()
{
    if(!isEulerian())
        return false;
    int v=1;
    do
    {
        euler(v);
        v = S.top(); S.pop();
        P.pb(v);
    }while(!S.empty());
    return true;
}

void writeCycle()
{
    TR( P, v)
        fout<<*v<<" ";
    fout<<"\n";
}

int main() {
    return 0;
    
    readGraph();
    
    if(fetchResult())
        writeCycle();
    else
        fout<<"-1";
    
}