#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
#define NMAX 100005
#define MMAX 500025

using namespace std;

int n, m, sol[NMAX], k, viz[MMAX];
vector <pair <int, int> > g[NMAX];
stack <int> s;

void read()
{
    scanf("%d%d", &n, &m);
    for(int i=1; i<=m; ++i)
    {
        int x, y;
        scanf("%d%d", &x, &y);
        g[x].push_back(make_pair(y, i));
        g[y].push_back(make_pair(x, i));
    }
}

void euler()
{
    s.push(1);
    int nod, indiceMuchie, fiu;
    while(!s.empty())
    {
        nod = s.top();
        if(!g[nod].empty())
        {
            indiceMuchie = g[nod].back().second;
            fiu = g[nod].back().first;
            g[nod].pop_back();
            if(viz[indiceMuchie] == 0)
            {
                viz[indiceMuchie] = 1;
                s.push(fiu);
            }
        }
        else
        {
            s.pop();
            printf("%d ", nod);
        }
    }
}

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

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