#include <fstream>
#include <vector>
using namespace std;

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

const int N=1e5+5, M=5e5+5;

int n, m;
bool viz[M];
vector<pair<int,int>> muchii;
vector<int> ad[N], sol;

void euler(int x)
{
    for(int v:ad[x]) if(!viz[v])
    {
        viz[v]=true;
        euler(muchii[v].first ^ muchii[v].second ^ x);
    }
    sol.push_back(x);
}

int main()
{
    fin>>n>>m;
    for(int i=0;i<m;++i)
    {
        int x, y;
        fin>>x>>y;
        muchii.push_back(make_pair(x, y));
        ad[x].push_back(i);
        ad[y].push_back(i);
    }

    for(int i=1;i<=n;++i)
    {
        if(ad[i].size()%2)
        {
            fout<<-1;
            return 0;
        }
    }

    vector<int> st;
    st.push_back(1);
    while(st.size())
    {
        int x=st.back();
        if(ad[x].size())
        {
            int v=ad[x].back();
            ad[x].pop_back();

            if(!viz[v])
            {
                viz[v]=true;
                st.push_back(muchii[v].first ^ muchii[v].second ^ x);
            }
        }
        else
        {
            sol.push_back(x);
            st.pop_back();
        }
    }

    for(unsigned i=0;i<sol.size()-1;++i)
    {
        fout<<sol[i]<<" ";
    }

    return 0;
}