#include <fstream>
#include <algorithm>
#include <vector>
#define N 100001
using namespace std;

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

vector <int> a[N], sol;
int s[N*2], sk;
int n, m;

void dfs(int x)
{
    int y;
    s[++sk]=x;
    while(sk)
    {
        x=s[sk];
        if(a[x].size())
        {
            y=a[x].back();
            a[x].pop_back();
            s[++sk]=y;
            a[y].erase(find(a[y].begin(), a[y].end(), x));
        }
        else
        {
            sk--;
            sol.push_back(x);
        }
    }
}

bool verif()
{
    for(int i=1;i<=n;i++)
    {
        if(a[i].size()%2) return 0;
    }
    return 1;
}

int main()
{
    int i, x, y;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        a[x].push_back(y);
        a[y].push_back(x);
    }
    if(verif())
    {
        dfs(1);
        for(i=0;i<sol.size()-1;i++)
        {
            fout<<sol[i]<<" ";
        }
    }
    else fout<<-1;
}