#include <fstream>
#include <vector>
#include <stack>
#include <queue>
using namespace std;
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

int n,m,d[100005],viz_noduri[100005],viz_muchie[500005],sol[500005],k;
vector<pair<int,int>>l[100005];
stack<int>s;
void dfs(int nod)
{
    viz_noduri[nod]=1;
    for(int i=0; i<l[nod].size(); i++)
    {
        int vecin=l[nod][i].first;
        if(viz_noduri[vecin]==0)
            dfs(vecin);
    }
}
void euler(int start)
{
    s.push(start);
    while(!s.empty())
    {
        int nod=s.top();
        while(!l[nod].empty() && viz_muchie[l[nod].back().second]==1)
            l[nod].pop_back();

        if(l[nod].empty())
        {
            sol[++k]=nod;
            s.pop();
        }
        else
        {
            viz_muchie[l[nod].back().second]=1;
            s.push(l[nod].back().first);
            l[nod].pop_back();
        }
    }
}
int main()
{
    cin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int x,y;
        cin>>x>>y;
        l[x].push_back({y,i});
        l[y].push_back({x,i});
        d[x]++;
        d[y]++;
    }
    dfs(1);
    for(int i=1; i<=n; i++)
        if(viz_noduri[i]==0 || d[i]%2!=0)
        {
            cout<<-1;
            return 0;
        }
    euler(1);
    for(int i=1; i<=k-1; i++)
        cout<<sol[i]<<" ";

    return 0;
}