#include <bits/stdc++.h>

using namespace std;
vector<pair<int,int>> e[100005];
vector<int> ans;
int deg[100005];
int n,m;
bool viz[100005];
void euler(int nod)
{
    while(!e[nod].empty())
    {
        int vc=e[nod].back().first;
        int edge=e[nod].back().second;
        e[nod].pop_back();
        if(!viz[edge])
        {
            viz[edge]=1;
            euler(vc);
        }
    }
    ans.push_back(nod);
}
int main()
{
    ifstream cin("ciclueuler.in");
    ofstream cout("ciclueuler.out");
    cin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int x,y;
        cin>>x>>y;
        e[x].push_back({y,i});
        e[y].push_back({x,i});
        deg[x]++;
        deg[y]++;
    }
    for(int i=1;i<=n;i++)
    {
        if(deg[i]%2)
        {
            cout<<"-1\n";
            return 0;
        }
    }
    euler(1);
    for(int i=0;i<m;i++)
        cout<<ans[i]<<" ";
    return 0;
}