// Ciclu eulerian - O(N+M) - ITERATIV
#include <fstream>
#include <vector>
#include <algorithm>
#include <stack>
#define Nmax 100009
#define pb push_back
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int N,M,x,y;
vector < int > G[Nmax],Cycle;
stack < int > st;

inline int IsEulerian()
{
    for(int i=1;i<=N;++i)
        if(G[i].size()&1)return 0;
    return 1;
}

void GetCycle(int S)
{
    for( st.push(S) ;!st.empty();)
    {
        int node=st.top();
        if(G[node].size()>0)
        {
            int last=G[node].back();
            st.push(last);
            G[node].pop_back();
            G[last].erase( find(G[last].begin(), G[last].end() , node)  );
        }
        else
        {
            Cycle.push_back(node);
            st.pop();
        }
    }
}

int main()
{
    f>>N>>M;
    for(int i=1;i<=M;++i)
        f>>x>>y , G[x].pb(y), G[y].pb(x);
    if(IsEulerian())
    {
        GetCycle(1);
        for(vector< int > ::iterator it=Cycle.begin();it!=Cycle.end();++it)
            g<<*it<<' ';
        g<<'\n';
    }
    else g<<-1<<'\n';
    f.close();g.close();
    return 0;
}