#include <stdio.h>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;
int n,m,i,x,y,nr[100001];
bool o[100001];
vector<int> G[100001],q;
void DFS(int s)
{
    int x;
    q.push_back(s);
    while (!G[s].empty())
    {
        x=G[s].back();
        G[s].pop_back();
        G[x].erase(find(G[x].begin(),G[x].end(),s));
        DFS(x);
    }

}
void conex(int s)
{
    int i,z=G[s].size();
    o[s]=1;
    for (i=0;i<z;i++)
        if (!o[G[s][i]]) conex(G[s][i]);
}
int main()
{
    freopen ("ciclueuler.in","r",stdin);
    freopen ("ciclueuler.out","w",stdout);
    scanf("%i%i",&n,&m);
    for (i=1;i<=m;i++)
    {
        scanf("%i%i",&x,&y);
        G[x].push_back(y);
        G[y].push_back(x);
        nr[x]++; nr[y]++;
    }
    conex(1);
    for (i=1;i<=n;i++)
        if (nr[i]%2!=0||!o[i]) {printf("-1"); return 0;}
    DFS(1);
    for (i=0;i<q.size()-1;i++) printf("%i ",q[i]);
    fclose(stdin);
    fclose(stdout);
    return 0;
}