#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
#define Nmax 100005

using namespace std;

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

int n, m;
vector <pair <int, int> > v[Nmax];
bitset <5*Nmax> seen;
vector <int> sol;

bool verif()
{
    for (int i = 1; i <= n; i++)
        if(v[i].size()%2 == 1) return 0;

    return 1;
}

void euler(int x)
{
    while(v[x].size()!=0)
    {
        int y=v[x].back().first;
        int c=v[x].back().second;
        v[x].pop_back();
        if(seen[c] == 1) continue;
        seen[c]=1;
        sol.push_back(y);
        euler(y);
    }
}

void print()
{
    for (vector <int> ::iterator it=sol.begin(); it!=sol.end(); it++)
        g << *it << " " ;
}

int main()
{
    f >> n >> m;
    for (int i = 1, x, y; i <= m; i++)
    {
        f >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }
    if(verif() == 0)
    {
        g << "-1\n";
        return 0;
    }
    euler(1);
    print();
    return 0;
}