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

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

const int limn = 100005;
const int limm = 500005;

int n, m, sol[limm], X[limm], Y[limm], k = 0;
bool B[limm];
vector<int> G[limn];

bool Euler()
{
    for(int i = 1; i <= n; ++i)
        if(G[i].size() & 1) return false;
    return true;
}

void DFS(int node)
{
    for(vector<int> :: iterator it = G[node].begin(); it != G[node].end(); ++it)
        if(!B[*it])
        {
            B[*it] = 1;
            DFS(X[*it] + Y[*it] - node);
        }
    sol[++k] = node;
}

int main()
{
    f >> n >> m;
    for(int i = 1; i <= m; ++i)
    {
        f >> X[i] >> Y[i];
        G[X[i]].push_back(i);
        G[Y[i]].push_back(i);
    }
    if(!Euler())    g << -1 << "\n";
        else
        {
            DFS(1);
            for(int i = 1; i < k; ++ i)
                g << sol[i] << " ";
        }
}