#include <bits/stdc++.h>
using namespace std;
struct muchie
{
    int x,y;
} edge[500007];
vector<int> v[100007],q;
char vaz[100007],elim[5000107];
void bfs(int nod)
{
    queue<int> q;
    vaz[nod]=1;
    q.push(nod);
    while(!q.empty())
    {
        int nod=q.front();
        q.pop();
        for(auto it=v[nod].begin(); it!=v[nod].end(); it++)
        {
            int vec=edge[*it].x^edge[*it].y^nod;
            if(!vaz[vec])
            {
                vaz[vec]=1;
                q.push(vec);
            }
        }
    }
}
void euler(int nod)
{
    while(!v[nod].empty())
    {
        int ind=v[nod].back();
        v[nod].pop_back();
        if(!elim[ind])
        {
            int vec=edge[ind].x^edge[ind].y^nod;
            q.push_back(nod);
            elim[ind]=1;
            nod=vec;
        }
    }
}
int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1; i<=m; i++)
    {
        scanf("%d%d",&edge[i].x,&edge[i].y);
        v[edge[i].x].push_back(i);
        v[edge[i].y].push_back(i);
    }
    bfs(1);
    for(int i=1; i<=n; i++)
        if(!vaz[i] || v[i].size()%2==1)
        {
            printf("-1");
            return 0;
        }
    int x=1;
    while(1)
    {
        euler(x);
        if(q.empty()) break;
        x=q.back();
        q.pop_back();
        printf("%d ",x);
    }
    return 0;
}