#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
#define NMAX 100005

using namespace std;

int N, M;
bool viz[NMAX * 5];
vector <pair <int, int> > G[NMAX];
vector <pair <int, int> >::iterator it;
stack <int> S;

void read()
{
    scanf("%d %d", &N, &M);
    for(int i=1; i<=M; ++i)
    {
        int a, b;
        scanf("%d %d", &a, &b);
        G[a].push_back(make_pair(b, i));
        G[b].push_back(make_pair(a, i));
    }
}

bool checkEuler()
{
    for(int i=1; i<=N; ++i)
        if(G[i].size() % 2)
            return false;
    return true;
}

void euler()
{
    S.push(1);
    int nod, indiceMuchie, vecin;
    while(!S.empty())
    {
        nod = S.top();
        if(!G[nod].empty())
        {
            indiceMuchie = G[nod].back().second;
            vecin = G[nod].back().first;
            G[nod].pop_back();
            if(viz[indiceMuchie] == false)
            {
                viz[indiceMuchie] = true;
                S.push(vecin);
            }
        }
        else
        {
            S.pop();
            printf("%d ", nod);
        }
    }
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    read();
    if(checkEuler())
        euler();
    else
        printf("-1");
    return 0;
}