#include <fstream>
#include <cstring>
#include <vector>
#include <algorithm>
#include <stack>
#include <iomanip>
#include <queue>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

#define nmax 100010
stack <int> stk;
vector <pair <int, int> > v[nmax];
vector <int> ans;
int i,n,m,nr;
bool useEdge[5*nmax];

int main()
{
    fin >> n >> m;
    for (i=1; i<=m; i++)
    {
        int a,b;
        fin >> a >> b;
        v[a].push_back(make_pair(b,i));
        v[b].push_back(make_pair(a,i));
    }
    for (i=1; i<=n; i++)
        if (v[i].size()%2!=0)
        {
            fout << "-1\n";
            return 0;
        }
    stk.push(1);
    while (!stk.empty())
    {
        int x=stk.top();
        while (v[x].size()>0)
        {
            while (v[x].size()>0&&useEdge[v[x][v[x].size()-1].second])
                v[x].pop_back();
            if (v[x].size()==0)
                break;
            int y=v[x][v[x].size()-1].first;
            useEdge[v[x][v[x].size()-1].second]=true;
            stk.push(y);
            x=y;
        }
        ans.push_back(x);
        stk.pop();
    }
    for (i=0; i<ans.size()-1; i++)
        fout << ans[i] << ' ';
}