#include<cstdio>
#include<list>

#define N_MAX 100010
#define M_MAX 500010
using namespace std;

list <int> G[N_MAX];

inline bool verif(int n)
{
    int i;
    for (i=1;i<=n;i++)
        if (G[i].size()%2==1) return false;
    return true;
}

inline void euler()
{
    int x,y;
    list <int> :: iterator it;
    x=1;
    while (!G[x].empty())
    {
        printf("%d ",x);
        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;
                }
        x=y;
    }
}
inline void load()
{
    int i,M,N,x,y;
    scanf("%d%d",&N,&M);
    for (i=1;i<=M;i++)
    {
        scanf("%d%d",&x,&y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    if (verif(N)) 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;
}