#include <iostream>
#include <stdio.h>
using namespace std;
FILE *f,*g;
struct graph
{
    int node, next;
}v[1000002];
int start[100002],deg[100002],st[100002];
int n,m;
void read()
{
    int x,y,k=0;
    fscanf(f,"%d %d",&n,&m);
    for(int i=1; i<=m; i++)
    {
        fscanf(f,"%d %d",&x,&y);
        v[++k].node=y;
        v[k].next=start[x];
        start[x]=k;
        v[++k].node=x;
        v[k].next=start[y];
        start[y]=k;
        deg[x]++;
        deg[y]++;
    }
}
void delete_edge(int a, int b)
{
    for(int i=start[a]; i; i=v[i].next)
        if(v[i].node==b)
        {
            v[i].node=-1;
            return;
        }
}
void solve()
{
    int vf,ok;
    for(int i=1; i<=n; i++)
        if(deg[i]%2!=0)
        {
            fprintf(g,"-1");
            return;
        }
    st[vf=1]=1;
    while(vf)
    {
        ok=0;
        for(int i=start[st[vf]]; i; i=v[i].next)
        {
            if(v[i].node!=-1)
            {
                start[st[vf]]=v[i].next;
                delete_edge(v[i].node, st[vf]);
                st[++vf]=v[i].node;
                v[i].node=-1;
                ok=1;
                break;
            }
        }
        if(!ok)
        {
           fprintf(g,"%d ",st[vf]);
           vf--;
        }
    }
}
int main()
{
    f=fopen("ciclueuler.in","r");
    g=fopen("ciclueuler.out","w");
    read();
    solve();
    fclose(f);
    fclose(g);
    return 0;
}