#include <iostream>
#include <stack>
#include <vector>
#include <cstdio>
#define N 500005

using namespace std;

struct muchie
{
    int viz, x, y;
}g[N];
int n, m;
vector <int> graf[N], sol;
stack <int> drum;

void citire()
{
    scanf("%d %d\n", &n, &m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d %d\n", &g[i].x, &g[i].y);
        g[i].viz=0;
        graf[g[i].x].push_back(i);
        graf[g[i].y].push_back(i);
    }
}

void ciclu_euler()
{
    drum.push(1);
    while(!drum.empty())
    {
        int nod=drum.top();
        if(graf[nod].size())
        {
            int nod2=graf[nod].back();
            graf[nod].pop_back();
            if(!g[nod2].viz)
            {
                g[nod2].viz=1;
                if(g[nod2].x==nod)
                    drum.push(g[nod2].y);
                else
                    drum.push(g[nod2].x);
            }
        }
        else
        {
            sol.push_back(drum.top());
            drum.pop();
        }
    }
}

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

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    citire();
    if(e_euler())
    {
        ciclu_euler();
        for(int i=0;i<sol.size()-1;i++)
            printf("%d ", sol[i]);
    }
    else
        printf("-1");
    return 0;
}