#include<cstdio>
#include<list>
#include<algorithm>
using namespace std;
int n,m,i,v,x,s[500001];
list<int> l[100001];
int main()
{
    freopen("ciclueuler.in","r",stdin),freopen("ciclueuler.out","w",stdout),scanf("%d%d",&n,&m);
    while(m--)
        scanf("%d%d",&i,&x),l[i].push_back(x),l[x].push_back(i);
    for(i=1;i<=n;++i)
        if(l[i].size()%2) {
            printf("-1");
            return 0;
        }
    for(v=s[1]=1;v;) {
        for(x=s[v];!l[x].empty();)
            i=l[x].front(),l[x].pop_front(),l[i].erase(find(l[i].begin(),l[i].end(),x)),s[++v]=x=i;
        printf("%d ",s[v--]);
    }
    return 0;
}