#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m;
bool viz[500005];
vector<pair<int,int>> v[100005];
vector<int>sol;

void euler(int x)
{
    while(!v[x].empty())
    {
        pair<int,int> i = v[x].back();
        v[x].pop_back();
        if(!viz[i.second])
        {
            viz[i.second] = 1;
            euler(i.first);
        }
    }
    sol.push_back(x);
}

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

    for(i = 1; i <= n; i++)
        if(v[i].size() != 0)
        {
            euler(i);
            break;
        }

    sol.pop_back();
    for(auto i : sol)
        fout<< i << " ";
    return 0;
}