#include <cstdio>
#include <vector>
#define nmax 100001
#define mmax 500001
using namespace std;

vector <int> a[nmax],st,v;
unsigned int v1[mmax],v2[mmax];
unsigned int n,m,x,i,j,nod,muchie;
bool viz[mmax];

void citire()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d",&n,&m);
    for(x=1;x<=m;x++)
    {
        scanf("%d %d",&i,&j);
        a[i].push_back(x);
        a[j].push_back(x);
        v1[x]=i;
        v2[x]=j;
    }
}

void afisare()
{
    for(x=0;x<v.size()-1;x++)
        printf("%d ",v[x]);
    printf("\n");
}

int main()
{
    citire();
    for(x=1;x<=n;x++)
        if(a[x].size()%2)
        {
            printf("-1\n");
            return 0;
        }
    st.push_back(1);
    while(!st.empty())
    {
        nod=st.back();
        if(!a[nod].empty())
        {
            muchie=a[nod].back();
            a[nod].pop_back();
            if(!viz[muchie])
            {
                viz[muchie]=true;
                if(nod==v1[muchie]) st.push_back(v2[muchie]);
                else st.push_back(v1[muchie]);
            }
        }
        else
        {
            st.pop_back();
            v.push_back(nod);
        }
    }
    afisare();
    return 0;
}