#include <cstdio>
#include <vector>
#include <stack>
using namespace std;
int i,j,m,n,x,y,nr;
stack <int> q,q1;
vector <int> v[100001];
void elr(int x)
{
    vector <int>::iterator it;
    vector <int>::iterator it1;
    int i,nr,y;
    if(!v[x].size()) {q1.push(x);q.pop();}
    else
    {it = v[x].begin();
    while( it!=v[x].end())
    {
        q.push(*it);
        if(!v[*it].empty()){
        for(it1=v[*it].begin(); it1!=v[*it].end()&&(*it1)!=x; it1++);
        if(*it1==x) v[*it].erase(it1);}
        y=*it;
        v[x].erase(it);
        elr(y);
    }}
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d",&n,&m);
    if(m%2==1) printf("-1\n");
    else{
    for(i=1; i<=m; i++)
    {
        scanf("%d %d",&x,&y);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    q.push(1);
    elr(1);
    while(!q.empty())
    {
        q1.push(q.top());
        q.pop();
    }
    while(!q1.empty())
    {
        if(q1.size()!=1) printf("%d ",q1.top());
        q1.pop();
    }
    }
    return 0;
}