#include <iostream>
#include <fstream>
#include <vector>
#define Nmax 100005

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n, m, x, y;
vector <pair<int, int> > v[Nmax];
vector <int> ans;
bool seen[Nmax];

void euler(int x)
{
    while(v[x].size())
    {
        int y = v[x].back().first;
        int edg=v[x].back().second;
        v[x].pop_back();
        if(seen[edg] == 1) continue;
        seen[edg]=1;
        euler(y);
    }
    ans.push_back(x);
}

int main()
{
    f >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        f >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }
    for (int i = 1; i <= n; i++)
        if(v[i].size()%2 == 1)
        {
            g << "-1";
            return 0;
        }
    euler(1);

    for (int i = 0, l=ans.size(); i < l; i++)
        g << ans[i] << " ";

    return 0;
}