#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

FILE *f=fopen("ciclueuler.in","r"),*g=fopen("ciclueuler.out","w");

const int maxn=100005;
int n,m,i,a,b,grad[maxn],k,copi,N;
bool viz[maxn],valid,in;
vector <int> x[maxn],afis;

void df(int nod)
{
    viz[nod]=true;
    for(int i=0;i<x[nod].size();i++)
        if(viz[x[nod][i]]==false)
            df(x[nod][i]);
}

int search(int a,int b)
{
    for(int i=0;i<x[b].size();i++)
        if(x[b][i]==a)
            return i;
}

void build()
{
    int nod=1,s=m;
    afis.push_back(nod);
    while(s)
    {
        in=false;
        for(i=0;i<x[nod].size();i++)
            if(x[nod][i]!=1)
            {
                copi=x[nod][i];
                afis.push_back(x[nod][i]);
                x[nod].erase(x[nod].begin()+i);
                x[copi].erase(x[copi].begin()+search(nod,copi));
                s--;
                nod=copi;
                in=true;
                break;
            }
            else
                copi=i;
        if(in==false)
        {
            if(x[nod].size())
            {
                afis.push_back(1);
                x[nod].erase(x[nod].begin()+copi);
                x[1].erase(x[1].begin()+search(nod,1));
            }
            s--;
            nod=1;
        }
    }
}

void write()
{
    for(i=0;i<afis.size()-1;i++)
    {
        for(;x[afis[i]].size(); afis.insert(afis.begin()+i,afis[i]) , x[afis[i]].erase(x[afis[i]].begin(),x[afis[i]].begin()+2));
        fprintf(g,"%d\n",afis[i]);
    }
    fprintf(g,"\n");
}

void read()
{
    fscanf(f,"%d%d",&n,&m);
    for(i=1;i<=m;i++)
    {
        fscanf(f,"%d%d",&a,&b);
        x[a].push_back(b);
        x[b].push_back(a);
        grad[a]++;
        grad[b]++;
    }
    valid=true;
    df(1);
    for(i=1;i<=n;i++)
        if(viz[i]==false||grad[i]%2==1)
            break;
    if(i<=n)
        valid=false;
    if(valid==true)
    {
        build();
        write();
    }
    else
        fprintf(g,"-1\n");
}

int main()
{
    read();
    return 0;
}