#include <fstream>
#include <vector>
#include <stack>

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n,m,x,y,i;
bool v[500005];
vector <pair<int ,int> >a[100004];
stack <int> q;
int main()
{
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        a[x].push_back({y,i});
        a[y].push_back({x,i});
    }
    for(i=1;i<=n;i++)
        if(a[i].size()%2)
        {
            fout<<-1;
            return 0;
        }
    q.push(1);
    while(q.size())
    {
        x=q.top();
        while(a[x].size()&&v[a[x].back().second])a[x].pop_back();
        if(a[x].empty())
        {
            fout<<x<<" ";
            q.pop();
        }
        else{
        q.push(a[x].back().first);
        v[a[x].back().second]=true;
        a[x].pop_back();
        }
    }
    return 0;
}