#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#define dMAX 100000

using namespace std;

int n, m, x, y;
bool viz;
vector<pair<int, bool> > graf[dMAX + 2];
vector<int> muchii;
int d[dMAX + 2];

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

bool Compare(pair<int, bool> e1, pair<int, bool> e2) {
    return e1.first < e2.first;
}

void Euler(int v) {
    int newV, u, l, nn;
    for (u = 0; u < graf[v].size(); u++) {
        newV = graf[v][u].first;
        viz = graf[v][u].second;
        if (!viz) {
            graf[v][u].second = true;
            for (l = 0; l < graf[newV].size(); l++) {
                nn = graf[newV][l].first;
                if (nn == v && graf[newV][l].second == false) {
                    graf[newV][l].second = true;
                    break;
                }
            }
            Euler(newV);
        }
    }
    muchii.push_back(v);
}

int main()
{
    int i, j;
    fin >> n >> m;
    for (i = 1; i <= m; i++) {
        fin >> x >> y;
        graf[x].push_back({y, 0});
        graf[y].push_back({x, 0});
        d[x]++, d[y]++;
    }
    /*for (i = 1; i <= n; i++) {
        if (d[i] % 2) {
            fout << -1;
            return 0;
        }
    }*/
    for (i = 1; i <= n; i++) {
        sort(graf[i].begin(), graf[i].end(), Compare);
    }
    //Euler(1);
    /*if (muchii.size() - 1 != m) {
        fout << -1;
        return 0;
    }*/
    //for (i = 0; i < muchii.size() - 1; i++) fout << muchii[i] << ' ';

    return 0;
}