#include <cstdio>
#include <vector>
#include <stack>

using namespace std;

const int nmx = 100002;
const int mmx = 500002;

struct muchie
{
    int nod1,nod2;
    bool sters = false;
} v[mmx];

int n,m;
vector <int> g[nmx];
stack <int> st;

void citire()
{
    scanf("%d %d", &n, &m);
    for(int i = 1; i <= m; ++i)
    {
        scanf("%d %d", &v[i].nod1, &v[i].nod2);
        g[v[i].nod1].push_back(i);
        g[v[i].nod2].push_back(i);
    }
}

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

void euler()
{
    st.push(1);
    while(not st.empty())
    {
        int nod = st.top();

        while(g[nod].size() && v[g[nod].back()].sters == true)
            g[nod].pop_back();

        if(g[nod].size())
        {
            int next = g[nod].back();
            g[nod].pop_back();
            v[next].sters = true;
            int next_nod = (nod == v[next].nod1 ? v[next].nod2 : v[next].nod1);
            st.push(next_nod);
        }
        else
        {
            printf("%d ", st.top());
            st.pop();
        }
    }
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    citire();
    if(nu_admite())
    {
        printf("-1\n");
        return 0;
    }
    euler();
    return 0;
}