#include <cstdio>
#include <list>
using namespace std;
int OK, i, N, M, x, y, Muchii[100001];
list<int> G[100001];
inline void DFS(int x)
{
    int i,y=x;
    list<int>::iterator it;

    while (!G[y].empty())
    {
        printf("%d ", y);
        i=G[y].back();
        G[y].pop_back();
        for (it=G[i].begin(); it!=G[i].end() && *it!=y; it++);
        G[i].erase(it);
        y=i;
    }
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    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);
        Muchii[x]++;
        Muchii[y]++;
    }
    OK=1;
    for (i=1; i<=N; i++)
        if (Muchii[i]%2==1) OK=0;
    if (!OK) printf("-1\n");
    else DFS(1);
    return 0;
}