#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;
        }
    }

    euler(1);

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

    return 0;
}