#include<cstdio>
#include<deque>
#include<list>

#define N_MAX 100010
using namespace std;

list<int> G[N_MAX];
deque<int> Q;

inline void euler()
{
    int i,y,x;
    list<int> :: iterator it;
    while (!Q.empty())
    {
        x=Q.front();
        if (G[x].empty())
                {
                    Q.pop_front();
                    printf("%d ",x);
                }
            else
                {
                    y=G[x].back();
                    G[x].pop_back();
                    for (it=G[y].begin();it!=G[y].end();it++)
                        if (*it==x)
                            {
                              G[y].erase(it);
                              break;
                            }
                }
    }
}

inline void load()
{
    int N,M,i,x,y;
    bool ok=true;
    scanf("%d%d",&N,&M);
    for (i=1;i<=M;i++)
    {
        scanf("%d%d",&x,&y);
        G[x].push_back(x);
        G[y].push_back(y);
    }

    for (i=1;i<=N;i++)
        Q.push_back(i);

    for (i=1;i<=N;i++)
        if (G[i].size()%2==1) ok=false;
    if (ok) euler();
        else printf("-1");
    printf("\n");
}

int main()
{
    freopen("ciceuler.in","r",stdin);
    freopen("ciceuler.out","w",stdout);
    load();
    fclose(stdin);
    fclose(stdout);
    return 0;
}