#include <fstream>
#include <queue>
#include <vector>
#include <algorithm>
#define pb push_back
#define nMax 100005
using namespace std;
ifstream fin("euler.in");
ofstream fout("euler.out");
vector<int> stck, G[nMax];
int n, m, ext[nMax];
void read()
{
    int a,b;
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        fin>>a>>b;
        G[a].pb(b);
        G[b].pb(a);
        ext[a]++;
        ext[b]++;
    }
}
void euler()
{
    stck.pb(1);
    while(!stck.empty())
    {
        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.pb(fiu);
        }
        else
        {
            fout<<stck.back()<<" ";
            stck.pop_back();
        }
    }
}
int main()
{
    read();
    for(int i=1;i<=n;i++)
        if(ext[i] & 1)
        {
            fout<<-1;
            return 0;
        }
    euler();
    return 0;
}