#include <fstream>
#include <list>
#include <algorithm>

using namespace std;

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

const int N = 100005;
int n, m, x, y, i;
list <int> ls[N];
int stiva[20*N], vf;

int main() {
    f >> n >> m;
    while (m--) {
        f >> x >> y;
        ls[x].push_back(y);
        ls[y].push_back(x);
    }

    for (i = 1; i <= n; i++)
        if (ls[i].size()%2) {
            g << -1;
            return 0;
        }

    stiva[vf=1] = 1;
    while (vf > 0) {
        x = stiva[vf];
        while (ls[x].empty() == 0) {
            y = ls[x].front();
            ls[x].pop_front();
            ls[y].erase( find(ls[y].begin(), ls[y].end(), x) );
            stiva[++vf] = y;
            x = y;
        }
        g << stiva[vf--] << ' ';
    }
}