#include <iostream>
#include <fstream>
#include <stdlib.h>
#include <time.h>
using namespace std;
int a[50][50],viz[50],n,m,gr[50];

void depth (int vf)

{
    int k;
    viz[vf]=1;
    for (k=1;k<=n;k++)
    {
        if (a[vf][k]!=0 && viz[k]==0)
            depth (k);
    }
}

int stergere(int x, int y)
{
    gr[x]--;
    gr[y]--;
    a[x][y]--;
    a[y][x]--;
}
int main()
{
    int i,j,c[50],x,y;
    srand(time(NULL)) ;
    ofstream g;
    ifstream f;
    f.open("ciclueuler.in");
    g.open("ciclueuler.out");
        f >> n >> m;
    for (i=1;i<=m;i++)
    {
        viz[i]=0;
        f>>x>>y;
        a[y][x]++;
        a[x][y]++;
        gr[x]++;
        gr[y]++;
    }
for (i=1;i<=n;i++)
{
    for (j=1;j<=n;j++)
    {
        c[i]=0;
        cout << a[i][j] << " ";
    }
    cout<< endl;
}
    depth(1);
    for (i=1;i<=n;i++)
        if (viz[i]==0)
        {
            g<<-1;
            return 0;
        }
        for (i=1;i<=n;i++)
            if (gr[i]%2==1)
            {
            g<<-1;
            return 0;
            }

    c[m]=1;
    y=m;
    while (m>=0)
    {
        for (j=1;j<=n;j++)
            if(a[c[m]][j]>0)
                if(gr[j]>1 || m==1)
                {
                    c[m-1]=j;
                    stergere(c[m],j);
                    break;
                }
        m--;
    }
   for (i=y;i>=0;i--)
        g<< c[i]<< " ";

}