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

using namespace std;

const string filename = "ciclueuler";
ifstream fin(filename + ".in");
ofstream fout(filename + ".out");

const int maxN = 100005;
int n, m;
bool viz[maxN], used[5 * maxN];

struct vec {
    int nod, ind;
};
vector <int> stiva;
vector <vec> G[maxN];

void dfs(int nod)
{
    if(viz[nod])
        return;
    viz[nod] = 1;
    for(vec vefin : G[nod])
        dfs(vefin.nod);
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        G[x].push_back({y, i});
        G[y].push_back({x, i});
    }
    dfs(1);
    bool valid = 1;
    for(int i = 1; i <= n; i++)
        if(G[i].size() % 2 == 1 || !viz[i])
            valid = 0;
    if(!valid)
    {
        fout << -1;
        return 0;
    }
    stiva.push_back(1);
    for(int i = 1; i <= m; i++)
    {
        int nod = stiva.back();
        while(!G[nod].empty())
        {
            vec vecin = G[nod].back();
            G[nod].pop_back();
            if(used[vecin.ind])
                continue;
            used[vecin.ind] = 1;
            nod = vecin.nod;
            stiva.push_back(nod);
        }
        fout << nod << ' ';
        stiva.pop_back();
    }
    return 0;
}