#include <fstream>
#include <vector>
#include <algorithm>

#define nMax 100001
#define pb push_back
using namespace std;

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

int n, m;
vector<int> stck, G[nMax];

int main()
{
    int a, b;
    fin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        fin>>a>>b;
        G[a].pb(b);
        G[b].pb(a);
    }

    for(int i=1; i<=n; i++)
    {
        if(G[i].size() & 1)
        {
            fout<<-1;
            return 0;
        }
    }
    stck.pb(1);
    while(stck.size())
    {
        int node=stck.back();
        if(G[node].size())
        {
            int fiu=G[node].back();
            G[node].pop_back();
            G[fiu].erase(find(G[fiu].begin(), G[fiu].end(), node));
            stck.push_back(fiu);
        }
        else
        {
            fout<<node<<" ";
            stck.pop_back();
        }

    }
}