#include <cstdio>
#include <iostream>
#include <vector>
using namespace std;
pair <int,int> v[500001];
int cnt;
int e[500001];
bool marcat[500001],viz[500001];
vector <int> a[100001];
const int dim=1<<17;
char getch()
{
    static char buff[dim];
    static int bp=dim;
    if(bp==dim)
    {
        bp=0;
        fread(buff,1,dim,stdin);
    }
    return buff[bp++];
}
void get(int &a)
{
    a=0;
    char ch;
    do
    {
        ch=getch();
    }
    while(ch<'0'||ch>'9');
    do
    {
        a=a*10+ch-'0';
        ch=getch();
    }
    while('0'<=ch&&ch<='9');
}
void dfs(int x)
{
    int muchie,y;
    viz[x]=1;
    for(int i=0; i<a[x].size(); i++)
    {
        muchie=a[x][i];
        y=v[muchie].second;
        if(x==y)
            y=v[muchie].first;
        if(!viz[y])
            dfs(y);
    }
}
void euler(int x)
{
    int muchie,y;
    for(int i=0; i<a[x].size(); i++)
    {
        muchie=a[x][i];
        if(!marcat[muchie])
        {
            marcat[muchie]=1;
            y=v[muchie].second;
            if(y==x)
                y=v[muchie].first;
            euler(y);
        }
    }
    e[++cnt]=x;
}
int main()
{
    ios::sync_with_stdio(0);
    cout.tie(0);
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    int n,m,i,x,y;
    get(n);
    get(m);
    for(i=1; i<=m; i++)
    {
        get(x);
        get(y);
        v[i].first=x;
        v[i].second=y;
        a[x].push_back(i);
        a[y].push_back(i);
    }
    dfs(1);
    for(i=1; i<=n; i++)
        if(!viz[i])
        {
            cout<<"-1";
            return 0;
        }
    for(i=1; i<=n; i++)
        if(a[i].size()%2)
            cnt++;
    if(cnt==0)
    {
        euler(1);
        for(i=1; i<=cnt-1; i++)
            cout<<e[i]<<" ";
    }
    else
        cout<<"-1";
    return 0;
}