#include <iostream>
#include <stdio.h>
#include <vector>
#include <algorithm>
#include <stack>

using namespace std;

const int N = 100001;

stack<int> s;
vector<int> v[N];

int n,m;

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d",&n,&m);
    int i,x,y,nod,aux;
    for(i=1;i<=m;i++)
    {
        scanf("%d %d",&x,&y);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    for(i=1;i<=n;i++)
        if(!v[i].size() || v[i].size()%2==1)
        {
            printf("-1");
            return 0;
        }
    s.push(1);
    while(!s.empty())
    {
        nod=s.top();
        if(!v[nod].size())
        {
            s.pop();
            if(!s.empty())
                printf("%d ",nod);
        }
        else
        {
            aux=v[nod].back();
            v[nod].pop_back();
            v[aux].erase(find(v[aux].begin(),v[aux].end(),nod));
            s.push(aux);
        }
    }
    return 0;
}