#include <bits/stdc++.h>

using namespace std;

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

int n,m,poz,x,y;
int euler[500005];
int viz[500005];
vector < pair<int,int> > la[100005];

void dfs(int from){
    while(la[from].size()){
        int to = la[from].back().first;
        int nr = la[from].back().second;

        la[from].pop_back();

        if(viz[nr])
            return;
        viz[nr] = 1;
        dfs(to);
    }

    euler[++poz] = from;
}

int main()
{
    in >> n >> m;
    for(int i = 1; i <= m; i++){
        in >> x >> y;
        la[x].push_back(make_pair(y, i));
        la[y].push_back(make_pair(x, i));
    }

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

    dfs(1);

    for(int i = 1; i < poz; i++)
        out << euler[i] << " ";

    return 0;
}