#include <stdio.h>
#include <vector>
#include <deque>
#include <bitset>

using namespace std;
FILE *f,*g;
vector <pair <int,int> > nod[100002];
deque <int> q;
bitset <500008> viz;
int n,m;
void eulerian(int no)
{
    int muchie,vecin;
    while(nod[no].size())///mai are vecini
    {
        muchie=nod[no].back().second;///ordinul muchiei
        vecin=nod[no].back().first;
        nod[no].pop_back();///eliminam vecinul
        if(!viz[muchie])///nu am mai trecut prin muchia asta
            viz[muchie]=1,eulerian(vecin);///mergem la urmatorul nod
    }
    q.push_back(no);///daca din nodul no nu mai putem merge in niciun alt nod, il introducem in coada finala
}

int main()
{
    int x,y;
    f=fopen("ciclueuler.in","r");
    g=fopen("ciclueuler.out","w");
    fscanf(f,"%d %d",&n,&m);
    for(int i=1;i<=m;++i)
    {
        fscanf(f,"%d %d",&x,&y);
        nod[x].push_back({y,i});///nodul x are ca si vecin nodul y si muchia dintre ele este de ordinul i;
        nod[y].push_back({x,i});///idem
    }
    for(int i=1;i<=n;++i)
        if(nod[i].size() % 2)///nodul i nu are grad par, deci nu admite ciclu Eulerian
        {
            fprintf(g,"-1\n");
            return 0;
        }
    eulerian(1);
    q.pop_back();
    while(!q.empty())
    {
        int x=q.front();
        fprintf(g,"%d ",x);
        q.pop_front();
    }
    fclose(f);
    fclose(g);
    return 0;
}