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#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

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


const int MAX_N = 100100;
const int MAX_M = 500100;

int n, m;
int grade[MAX_N];

bool vis[MAX_M];

int x[MAX_M], y[MAX_M];

vector<int> g[MAX_N];


inline void euler(const int &node) {

    int _size = g[node].size();
    while (_size) {
        int i = g[node][--_size];

        g[node].pop_back();
        if (!vis[i]) {
            vis[i] = true;
            euler(x[i] + y[i] - node);
        }
    }
    fout << node << ' ';
}


int main() {
    fin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        fin >> x[i] >> y[i];
        g[x[i]].push_back(i);
        g[y[i]].push_back(i);
        ++grade[x[i]];
    }
    fin.close();

    for (int i = 1; i <= n; ++i)
        if (grade[i] & 1) {
            fout << "-1\n";
            fout.close();
            return 0;
        }

    euler(1);
    fout.close();

}