#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

const int MAXN = 100005, MAXM = 500005;

vector<pair<int, int> > graf[MAXN];
vector<int> ans;
int grad[MAXN];
bool vis[MAXM];

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

int n, m;

stack<int> euler;

int main()
{
    fin >> n >> m;
    int x, y;
    for(int i = 1; i <= m; ++i){
        fin >> x >> y;
        grad[x]++;
        grad[y]++;
        graf[x].push_back({y, i});
        graf[y].push_back({x, i});
    }
    bool ok = 1;
    for(int i = 1; i <= n && ok; ++i)
        if(grad[i] % 2 || grad[i] == 0)
            ok = 0;
    if(ok){
        euler.push(1);
        while(!euler.empty()){
            int nod = euler.top();
            if(graf[nod].size()){
                int next = graf[nod].back().first, edge = graf[nod].back().second;
                graf[nod].pop_back();
                if(!vis[edge]){
                    vis[edge] = 1;
                    euler.push(next);
                }
            }
            else{
                ans.push_back(nod);
                euler.pop();
            }
        }
        ans.pop_back();
        for(int i = 0; i < int(ans.size()); ++i)
            fout << ans[i] << " ";
    }
    else
        fout << -1;
    return 0;
}