#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
stack < int >q;
vector < int >a[1000000],sol;
int n,m,ok,x,y;

void euler(int start)
{
    q.push(start);
    while(q.size())
    {
        int nod=q.top();
        if(a[nod].size())
        {
            int last=a[nod].back();
            q.push(last);a[nod].pop_back();
            a[last].erase(find (a[last].begin(),a[last].end(),nod));
        }
        else q.pop(),sol.push_back(nod);
    }
}

int main()
{
    f>>n>>m;
    for(int i=1; i<=m; i++)
    {
        f>>x>>y;
        a[x].push_back(y);
        a[y].push_back(x);

    }

    for(int i=1; i<=n; i++)
        if(a[i].size()%2==1){ok=1;break;}
    euler(1);
    if(ok==1)g<<-1;
        else for(int i=0; i<sol.size(); i++)
            g<<sol[i]<<" ";
    return 0;
}