#include <fstream>
#include <vector>
#include <algorithm>
#include <queue>

using namespace std;

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

vector <int> ls[100005];
int n, m, x, y, i, l;
bool viz[100005];
int stiva[120005], vf;

void bf(int x) {
    int i;
    queue<int>c1;
    c1.push(1);
    while (c1.empty() == 0) {
        x = c1.front();
        l = ls[x].size();
        c1.pop();
        for (i = 0; i < l; i++) {
            y = ls[x][i];
            if (viz[y] == 0) {
                viz[y] = 1;
                c1.push(y);
            }
        }
    }
}

int main() {
    f >> n >> m;
    while (m--) {
        f >> x >> y;
        ls[x].push_back(y);
        ls[y].push_back(x);
    }
    bf(1);
    for (i = 1; i <= n; i++)
        if (ls[i].size()%2 == 1 || viz[i] == 0) {
            g << -1;
            return 0;
        }
    stiva[(vf=1)] = 1;
    while (vf>0) {
        x = stiva[vf], l = ls[x].size();
        if (l == 0) {
            g << x << ' ';
            vf--;
            continue;
        }
        y = ls[x][l-1];
        stiva[++vf] = y;
        ls[x].pop_back();
        ls[y].erase(find(ls[y].begin(),ls[y].end(), x));
    }

    return 0;
}