#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
#include <stack>
#include <tuple>

using namespace std;

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

const int MaxE = 500001;

using VI = vector<int>;
using VT = vector<tuple<int, int>>;
using IT = VT::iterator;
using VIT = vector<IT>;
using VVT = vector<VT>;

bitset<MaxE> v;
VVT G; ///G[i] - vector de muchii (hehe xD)
VI ce;
int n, m;

void Citeste();
void Afiseaza();
bool EsteEulerian();
void Determ(int x);

int main()
{
    Citeste();
    if(!EsteEulerian())
        fout << -1;
    else
    {
        Determ(1);
        Afiseaza();
    }

    return 0;
}

void Citeste()
{
    fin >> n >> m;
    G = VVT(n + 1);

    int a, b;
    for(int i = 1; i <= m; ++i)
    {
        fin >> a >> b;
        G[a].emplace_back(b, i);
        G[b].emplace_back(a, i);
    }
}
void Afiseaza()
{
    for(size_t i = 0; i < ce.size() - 1; ++i)
        fout << ce[i] << ' ';
}

bool EsteEulerian()
{
    for(int x = 1; x <= n; ++x)
        if(G[x].size() % 2 == 1)
            return false;
    return true;
}

void Determ(int x)
{
    VIT p = VIT(n + 1);
    for(int i = 1; i <= n; ++i)
        p[i] = G[i].begin();

    int y, e;
    stack<int> stk;
    stk.push(1);

    while(!stk.empty())
    {
        x = stk.top();
        if(p[x] == G[x].end())
        {
            ce.emplace_back(x);
            stk.pop();
        }
        else
            while(p[x] != G[x].end())
            {
                tie(y, e) = *p[x]++;
                if(v[e]) continue;
                v[e] = 1;
                stk.push(y);
                break;
            }
    }
}